Thin Film Semiconductor-on-Glass Solar Cell Devices

ABSTRACT

The present invention relates to semiconductor devices suitable for electronic, optoelectronic and energy conversion applications. In a particular form, the present invention relates to the fabrication of a thin film solar cells and thin film transistors through the advantageous combination of semiconductors, insulators, rare-earth based compounds and amorphous and/or ceramic and/or glass substrates. Example embodiments of crystalline or polycrystalline thin film semiconductor-on-glass formation using rare-earth based material as impurity barrier layer(s) are disclosed. In particular, thin film silicon-on-glass substrate is disclosed as the alternate embodiment, with impurity barrier designed to inhibit transport of deleterious alkali species from the glass into the semiconductor thin film.

PRIORITY

This application is a continuation of U.S. application Ser. No.12/119,387, filed on May 12, 2008 and claims priority from Provisionalapplication 60/944,369 filed on Jun. 15, 2007.

CROSS REFERENCE TO RELAYED APPLICATIONS

Applications and patent Ser. Nos. 09/924,392, 10/666,897, 10/825,912,10/825,974, 11/025,363, 11/025,681, 11/025,692, 11/025,693, 11/084,486,11/121,737, 11/187,213, 11/053,775, 11/053,785, 11/054,579, 11/068,222,11/188,081, 11/253,525, 11/254,031, 11/393,629, 11/398,910, 11/472,087,11/788,153, 11/960,418, 12/119,387, 60/820,438, 60/811,311, 60/847,767,60/905,419, 60/905,945, 60/944,369, 60/949,753, U.S. Pat. No. 7,018,484,U.S. Pat. No. 7,037,806, U.S. Pat. No. 7,135,699, U.S. Pat. No.7,199,015, all held by the same assignee, contain information relevantto the instant invention and are incorporated herein in their entiretyby reference. References, noted at the end, are incorporated herein intheir entirety by reference.

BACKGROUND OF THE INVENTION

Prior art concerning solar cells and thin film transistors, TFTs, areknown to one knowledgeable in the art. References contained in U.S. Pat.No. 4,128,733, U.S. Pat. No. 6,743,974, U.S. Pat. No. 7,030,313, U.S.2002/0040727, U.S. 2005/0000566 are cited as prior art and incorporatedherein in their entirety by reference. The present invention addressesthe need to increase solar cell efficiency and to further reduce costover prior art techniques.

Typically, the use of low cost substrates places limitation upon thinfilm semiconductor crystal quality and/or thermal budget required forthin film deposition method of a thin film(s). Low thermal budgetdeposition of thin films typically results in poor crystal qualitysemiconductors realized upon amorphous glass substrates. Singlesemiconductor crystals may nucleate in localized areas upon an initialglass substrate surface, but formation of homogeneous and long rangecrystal order within the thin film across substantially the entire largearea glass substrate is practically impossible without complex postgrowth recrystallization. Even so, the film quality attained using priorart complex recrystallization techniques is still inferior to bulksingle crystal growth techniques, such as, the Czochralski crystalgrowth (CZ) method.

Single crystal thin film epitaxy is typically done on substrates withintrinsic properties of high single crystal quality, atomically flatsurface, and low crystal structure mismatch between the film andsubstrate. More desirable of the polycrystalline forms are thin filmsemiconductors exhibiting large domains (grain size ˜0.1-10 microns) inlateral and/or vertical dimensions relative to the film growthdirection. Thin films exhibiting larger lateral grain dimension thanfilm thickness enable advantageous transport of electronic carriersparallel to the film/substrate surface. Direct deposition of thin filmsemiconductors onto glass substrates without complex post processingresults in polycrystalline (pc), microcrystalline (mc), nanocrystalline(nc) and/or amorphous (a) semiconductor thin films.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to semiconductor devices combined with aninexpensive substrate for electronic and optoelectronic applications. Ina particular form the present invention relates to fabrication of asolar cell and/or thin film transistor (TFT) through the combination ofrare-earth metal, rare-earth metal-oxides-nitrides, -phosphides and-carbides and Group IV, III-V, and II-VI semiconductors and alloysdisposed upon inexpensive substrates, such as glass. In an embodiment,thin film semiconductor materials composed of silicon (Si) and/orgermanium (Ge) are disposed upon cost effective silicon dioxide (SiO₂)based glass substrate. Such semiconductor-on-glass (SoG) articles areapplicable to thin film transistor and solar cell manufacture. Thepresent invention discloses the use of a functional barrier layerdisposed between a thin film semiconductor layer and an inexpensivesubstrate so as to inhibit transport and deleterious action of impurityspecies migrating from the substrate into a thin film semiconductor,thereby degrading the electronic and/or optical performance of the saiddevice. Optionally, a functional barrier layer may serve as analternative barrier between an inexpensive substrate and a functionaldevice disposed thereon; examples of types of barriers are thermal,mechanical, chemical, optical, and/or other radiation deleterious to afunctional device and/or from a device to its substrate.

Thin film semiconductor-on-glass application to solar cell and TFTdevices benefit from the insulating nature of the glass substrate andcan be designed as ideal thin film semiconductor-on-insulator (SOI)structures. For mass manufacture of SoG the utility of a glass substrateis primarily due to the potential low cost of alkali-silicate glasses.However, it has long been known by workers in the field of glassmanufacture that most compositions of alkali-silicate glasses exhibitsome electrical conductivity. The electrical activity of thealkaline-silicate glasses is directly attributable to mobile positivealkaline ions through the silicate network; in addition inexpensiveglasses may contain high levels of boron, lead and other elementsinjurious to a semiconductor. Optional inexpensive substrates containalternative elements not acceptable to a solid-state device; in generalsome type of barrier must isolate a semiconductor device from someproperty of an inexpensive substrate.

It is an object of one embodiment of the present invention to fullyutilize the low cost of alkaline-silicate glasses for use in SoG andincrease the performance of devices formed by use of alkaline barrierlayers. An example embodiment, but not limited to, is the use ofrare-earth compound(s), such as a rare-earth oxide (REO_(x)), comprisingcharged oxygen vacancies (O_(v) ^(n)) capable of neutralizing themigration of deleterious positive alkaline ions, such as Na⁺ and/or K⁺,into a semiconductor active region; charged oxygen vacancies (O_(v)^(n)) functionally impede migration of positive ions to the extent thatan active region above a barrier layer functions within specification.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A depicts schematically the physical MOS layer structure formed ona SoG substrate and FIG. 1B depicts the energy band structure of the MOSSoG device as a function of cross-sectional distance vertically throughthe layers.

FIG. 2A shows the use of a barrier layer in a modified MOS SoGstructure; FIG. 2B, shows a criteria for an alkali barrier layer whichis the advantageous partitioning of the valence (ΔE_(v)) and conduction(ΔE_(c)) band.

FIG. 3 shows the geometry used for ion implantation of foreign speciesinto preferentially CZ Si substrate.

FIG. 4 shows depth profiles for H+ ions using various incident energyimplants.

FIG. 5 shows exemplary ion implantation into an original devicesubstrate.

FIG. 6 shows exemplary ion implantation into an original devicesubstrate.

FIG. 7 shows the distribution of H⁺ ions 701 in the buried layer beneaththe Si surface for the case of 3 MeV.

FIGS. 8A and B show individual parallel process paths for fabrication ofthin film single crystal solar cell on glass article.

FIGS. 9A and B show how an alternative or replacement substrate withinsulating and/or conductive barrier layers and implanted CZ Sisubstrate are joined together.

FIGS. 10A and B show how a compound multilayer article is subjected to athermal annealing sequence.

FIG. 11 shows how, with application of external mechanical stimulus toat least one region of the edge of the compound article, the fracturepropagates throughout the defect plane.

FIG. 12 shows how a wafer bonded thin film CZ Si forms a buried barrierlayer on a glass substrate and are then processed to form a verticaltype MIS.

FIG. 13 discloses an example method and general process flow forfabricating multiple single crystalline semiconductor layers.

FIG. 14 shows a remaining portion of a silicon thin film separated fromthe bulk of a substrate via defect layer.

FIG. 15 shows a transferred layer stack forming a p-i-n-i-p doped Simultilayer diode coupled to a glass substrate.

FIG. 16A shows the overlap of Ge absorption with the solar spectrum and16B shows the energy band structure of bulk single crystal Si as afunction of energy.

FIG. 17A shows a metal-insulator-semiconductor (MIS) device fabricatedupon a glass substrate; FIG. 17B shows an equivalent circuit.

FIG. 18A shows multiple lateral devices connected via a common activelayer contact; FIG. 18B shows an equivalent circuit.

FIG. 19A is an p-i-n SoG embodiment; FIG. 19B shows an equivalentcircuit.

FIG. 20A shows multiple lateral p-i-n devices fabricated across the SoGsubstrate;

FIG. 20B shows p-i-n devices series connected.

FIG. 21A is a stacked layer structure consisting of two p-i-n diodescomprising different intrinsic absorber thicknesses. FIG. 21B shows thegeneration rate G (λ, z) of electron-hole pairs as a function ofvertical distance, z, through a layered structure.

FIGS. 22A and 22B show wavelength bands 2300 & 2310 used for an exampletandem Si: p-i-n-p-i-n solar cells.

FIG. 23 discloses a MIS/PIN hybrid.

FIG. 24A: Process steps for epitaxial deposition of single crystalarticle containing thin film semiconductor and sacrificial layer.

FIG. 24B: Selective modification of sacrificial layer via lateralprocess.

FIG. 24C: Transformation of single crystal sacrificial layer viaselective process.

FIG. 25A: Process of forming single crystal article comprising thin filmsemiconductor and sacrificial layer. Parallel process of preparingalternative substrate for wafer bonding to exposed thin filmsemiconductor or interfacial bonding layer surface.

FIG. 25B: Process steps of wafer bonding alternative substrate to singlecrystal article.

FIG. 25C: Process steps showing selective lateral modification ofsacrificial layer contained in composite article.

FIG. 26: Process paths for thin film semiconductor layer separation byaction of sacrificial layer in composite article.

FIG. 27: Chemical processes for modifying crystal structure of singlecrystal rare-earth oxide by means of hydrogenation, carbonization andhydration.

FIG. 28: Catalytic layer separation using rare-earth based layercomprising alternative substrate and thin film semiconductor layer.

FIG. 29: Crystal structure modification of process using rare-earthbased compound.

FIG. 30: Single crystal rare-earth based sacrificial layer underselective etching or removal via incident species, ultimately leavingthe exposed substrate.

FIG. 31: Process steps for selective area single crystal thin filmsemiconductor and sacrificial layer epitaxy on parent substrate.

FIG. 32: Process steps for wafer bonding selective area single crystalthin film regions on parent substrate with alternative substrate.

FIG. 33: Process steps showing selective area thin film semiconductor onalternative substrate layer separation via action of release throughremoval of sacrificial layer.

FIG. 34: Schematic description of selective area thin film semiconductoron alternative substrate and fabricated electronic and or optoelectronicdevices formed from thin film semiconductor regions.

FIG. 35: Process steps for further deposition of thin filmsemiconductor(s) upon patterned thin film single crystal semiconductoron alternative substrate.

FIG. 36: Two junction solar cell formed from crystalline and amorphoussemiconductor devices disposed upon alternative substrate.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is the manufacture of thin filmsemiconductor-on-glass suitable for high performance thin filmtransistors and solar energy conversion devices. It is understood thepresent invention is applicable to other substrate compositions otherthan glass, such as polymers, metals, ceramics, and biologically activesubstrates and the like.

Furthermore, the present invention discloses alternate embodiments ofthin film semiconductors chosen from at least one of silicon (Si),germanium (Ge), silicon-carbide (SiC_(x)), germanium carbide (GeC_(x)),germanium nitride (GeN_(x)), silicon nitride (SiN_(x)) tin germanium(SnGe_(x)), tin oxide (SnO_(x)), gallium phosphide (GaP), galliumnitride (GaNx), indium nitride (InNx), aluminium nitride (AlNx), zincoxide (ZnO_(x)), magnesium oxide (MgO_(x)) or combinations andnon-stoichiometric combinations thereof wherein x varies from >0 to ≦20in some embodiments.

For example, GaN-based and ZnO-based compositions are advantageous forlight emitting diode applications disposed upon glass substrates.Compositions such as (i) Si_(x)Sn_(y)Ge_(z)C_(w); (ii)In_(x)Ga_(y)Al_(z)N_(w); and (iii) Zn_(x)Mg_(y)O_(z)N_(w) are alsodisclosed by the present SoG invention wherein w, x, y, z vary from 0 to≦1 in some embodiments.

Alternative embodiments use Si, Ge and SiGe thin film semiconductorcompositions for SoG article manufacture of TFT and solar cell devicesdisposed upon cheap glass and/or ceramic substrates.

A general formula for oxide glass, but not limiting, may be written forconvenience as A_(n)B_(m)O_(z), where B represent the network formingcation(s), A the modifying cation(s), O is oxygen, and the real positivenumbers m, n, z represent relative chemical ratios varying from 0 to ≦1;it is understood that additional impurities are present. If the A ionsare introduced into silica where B=Si, in the form of an oxide forexample A_(k)O_(y); then A_(n)SiO_(z)=(A_(k)O_(y))_(x).(SiO₂)_(1-x). Forexample, the structure modifying A cations may act so as to plug holesin the network formed by the B_(m)O_(z). For example, alkali silicateglass (A_(n)Si_(m)O_(z)), use relatively large cations of low chargee.g., A chosen from at least one of the set {Na⁺, K⁺, Li⁺, Ca²⁺, Ba²⁺,Pb²⁺, and the like}.

The silicate glasses are the most technologically and commerciallyapplicable material for the present invention, namely, low cost and highvolume manufacture thin film semiconductor-on-glass for use in solarenergy conversion and display devices. The soda-lime-silica glass(SLSG), boro-silicate glass (BSG) and boro-phosphate-silicate glass(BPSG) are exemplary compositions for application to the presentinvention. It is also understood, other compositions are equally coveredby the present invention, for example, alumino-silicate glass (ASG),alkaline-earth silicate (AESG) glass and fluorine and/or chloridecontaining silicate glasses.

High purity quartz substrates are composed of pure SiO₂, but areexpensive compared to silicate glass substrates which are typicallycomposed of only a majority of silica, SiO₂,30-75%. Herein defined asSiO₂-based glass. Therefore, SoG devices fabricated on pure quartzsubstrates will not typically suffer thin film contamination due to thesubstrate; however a barrier layer as used herein may serve as a bufferlayer on quartz as a means to transition to a single crystal activestructure. Cost effective technical glasses useful for manufacture offlat panel displays, TFTs, solar cells, light emitting devices and thelike, typically contain additional compounds, such as, calcium oxide(CaO), sodium oxide (Na₂O), potassium oxide (K₂O), aluminum oxide(Al₂O₃), boron oxide (B₂O₃), zirconium oxide (ZrO₂), zircon (ZrSiO₄),fluorine, lithium, lead oxide (PbO), alkaline earth metal oxides (AEOx),transition-metal oxides (e.g., TiO₂) and others to a lesser extent.

Alkali ionic conduction in glass, and in particular silicate glasses isa well studied process. Multi-component alkali silicate glasses havehistorically been developed primarily for improving glass formationproperties suitable for various manufacturing tolerances, increasingmechanical and/or optical performance. For example, the addition of CaOinto silicate glass introduces Ca²⁺ ions forming relatively strongerCa—O bonds compared to Na—O bonds. The Ca²⁺ ions are held more firmly inthe structure and believed to improve chemical durability of a glass.Addition of larger cations, via introducing CaO and MgO into theNa₂O.SiO₂ glass increases stability of glass and allows it to be madewith a lower SiO₂ content and improve glass forming temperature andregion and devitrification properties. Regardless of the multi-alkaliglass, it is generally found that the dominant species responsible forionic conduction is due to sodium ions. The consequence of ionicconduction in silicate glasses is becoming particularly problematic inSoG device manufacture, where the finite conductivity and variation ofproperties of thin films occurs when in contact with a silicate glass.

In microelectronic and/or silicon integrated circuit manufacture it iswell established the presence of mobile contaminants in group IVsemiconductor (e.g.; Si) and dielectric processing (e.g.; SiO₂),particularly the presence of sodium ions (Na⁺) and potassium ions (K⁺)ions are extremely detrimental to device performance and yield.Borosilicate glasses are not used in Si semiconductor processing due tonot-intentional boron doping effects. Sodium is extremely mobile insilica and thermally grown SiO₂ on Si and within low dielectricinterconnect layers. The presence of alkali ions, such as Na⁺, in gateoxide and near SiO₂/Si interfaces of Si-based metal-oxide-semiconductorfield effect transistors (MOSFETs) cause electronic defects, traps, flatband voltage shifts, and reliability and instability issues at highoperating temperatures and/or processing temperatures. Positive ions(e.g.; alkali ions such as Na⁺, K⁺ and Li⁺ or alkaline earth ions, suchas Mg²⁺, Ca²⁺, Ba²⁺, Sr²⁺) can move relatively freely within glassand/or SiO₂ dielectric in response to an applied electric field and/orthermal gradient, thereby forming a source of mobile ionic charge.Significant effort is made to remove sources of sodium and/or alkalicontamination judiciously from Si semiconductor processing. Theremaining and persistent alkali contamination within upper levelinterconnect layers is mitigated in part via the use of phosphate glass(e.g.; P₂O₅), phosphorous silicate glass (e.g.; P₂O₅.SiO₂) and siliconnitride compositions.

The presence of alkali ions disadvantageously affects performance ofmetal-insulator-semiconductor (MIS) devices, such as solar MIS solarcells and TFTs based on semiconductor-dielectric MOSFETs. It is oneobject of the present invention to use alkali barrier layer(s) in MISsolar cells fabricated from a SoG article.

A solution to sodium permeability in glass compositions, in particular,quartz and silica, has been disclosed in U.S. Pat. No. 5,631,522. Theintentional doping of the low sodium containing glass with aluminum(Al), yttrium (Y), cesium (Cs) and mixtures thereof, has been shown todramatically reduce sodium diffusion through the doped glass used insodium containing metal halide lamps. It is disclosed herein that triplyionized rare-earth metal ions, such as lanthanum (La) and erbium (Er),typically in the form of rare-earth sesquioxides oxides, can be added toa Si lattice of Cs or Y doped SiO₂ glass to further minimize the sodiumdiffusivity. The instant invention discloses the permeability of sodiumin glass can be lowered by advantageous doping of the SiO₂ glass by theaddition of at least one of Al, Cs, La, Dy, and/or Er and/or other rareearth metals, oxides, nitrides, phosphides and/or combinations thereof.

Economical alkali-silicate glasses are composed of the very impuritiesthat are detrimental to TFT and solar cell performance. Therefore, it isdesirable for a simple and cost effective method to be implemented inorder to contain the impurities within the glass substrate, such asmobile alkali ions, so as not to degrade the performance of electronicdevices based on thin film semiconductors disposed upon the said glasssubstrate.

The present invention discloses and claims the use of at least onealkali impurity barrier layer for SoG article manufacture wherein thebarrier layer is disposed between semiconductor thin film(s) and a glasssubstrate.

The present invention claims the use of barrier layers, as describedabove, for all SoG manufacturing techniques used to form single crystal,polycrystal and/or amorphous thin film semiconductors. For example, SoGarticle manufactures using: (i) single crystal semiconductor thin filmtransferred via wafer bonding; or (ii) direct epitaxy of amorphoussemiconductor; or (iii) direct epitaxy of amorphous-semiconductor andsubsequent recrystallisation; or (iv) direct epitaxy of polycrystallinesemiconductor; (v) direct epitaxy of single crystalline semiconductor ona rare-earth based buffer layer(s).

The present invention discloses and claims the preferential use ofbarrier materials for SoG manufacture using rare-earth sesquioxide(RE₂O₃), rare-earth dioxide (REO₂), rare-earth monoxide (REO),rare-earth nitride (REN), rare-earth oxynitride (REO_(x)N_(y)),rare-earth phosphide (REP), rare-earth oxyphosphide (REO_(x)P_(y)),rare-earth carbide (REC_(y)), rare-earth oxycarbide (REO_(x)C_(y)),aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)), and rare-earthaluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), aluminum oxide (Al₂O₃),silicon nitride (SiN_(x)), (Si_(x)Al_(y)N_(z)) and combinations andnon-stoichiometric combinations thereof. A barrier material may compriseone or more layers; wherein at least one layer comprises at least onecompound chosen from a group comprising a rare-earth sesquioxide(RE₂O₃), rare-earth dioxide (REO₂), rare-earth monoxide (REO),rare-earth nitride (REN), rare-earth oxynitride (REO_(x)N_(y)),rare-earth phosphide (REP), rare-earth oxyphosphide (REO_(x)P_(y)),rare-earth carbide (REC_(y)), rare-earth oxycarbide (REO_(x)C_(y)),aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)), and rare-earthaluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), aluminum oxide (Al₂O₃),silicon nitride (SiN_(x)), (Si_(x)Al_(y)N_(z)) and combinations andnon-stoichiometric combinations thereof; wherein 0≦w, x, y, z≦1 asrequired to make a predetermined compound of suitable functionality.

A barrier material may comprise one or more layers; wherein at least onelayer comprises at least one compound chosen from a group comprising[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >0. Abarrier material may be single crystalline; optionally it may bepolycrystalline; optionally it may be amorphous; optionally barriermaterial may comprise one or more layers, at least one of which issingle crystal.

The invention discloses the steps of:

a. preparing a clean glass substrate surface,b. depositing barrier layer(s) upon a glass surface, chosen fromcompositions of at least one of a rare-earth sesquioxide (RE₂O₃),rare-earth dioxide (REO₂), rare-earth monoxide (REO), rare-earth nitride(REN), rare-earth oxynitride (REO_(x)N_(y)), rare-earth phosphide (REP),rare-earth oxyphosphide (REO_(x)P_(y)), rare-earth carbide (REC_(y)),rare-earth oxycarbide (REO_(x)C_(y)), aluminium rare-earth oxide(RE_(x)Al_(y)O_(w)), and rare-earth aluminosilicate(RE_(x)Al_(y)Si_(z)O_(w)), aluminum oxide (Al₂O₃), silicon nitride(SiN_(x)), (Si_(x)Al_(y)N_(z)) and combinations thereof,c. forming a thin film semiconductor layer on the barrier layer/glasssubstrate composite article with the barrier layer disposed between thethin film and the glass substrate.

The described SoG article can be formed using layer transfer and/ordirect wafer bonding and/or direct deposition and/or recrystallization.The SoG article may comprise semiconductor and/or barrier layers chosenfrom substantially single crystal and/or polycrystalline and/ormicrocrystalline and/or nanocrystalline and/or amorphous thin filmcrystal structure. I rare-earth barrier layer may be deposited on asemiconductor prior to attachment to a glass substrate.

Specifically, for solar cell operation it is desirable the glasssubstrate function as the environmental barrier for the thin filmsemiconductor and also as an optically transmissive coating for low losssolar spectrum absorption into the said semiconductor. Therefore, it isdesirable for a barrier layer to exhibit optical transparency to solarradiation. That is, a barrier layer is chosen to exhibit a large bandgap in excess of about 3 eV. In preference, barrier layer compositionsof rare-earth sesquioxide (RE₂O₃), rare-earth dioxide (REO₂), rare-earthmonoxide (REO), rare-earth oxynitride (REO_(x)N_(y)), rare-earthoxyphosphide (REO_(x)P_(y)), rare-earth oxycarbide (REO_(x)C_(y)),aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)), and rare-earthaluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), aluminum oxide (Al₂O₃),silicon nitride (SiN_(x)), (Si_(x)Al_(y)N_(z)) and combinations thereof.

A rare-earth metal can be chosen from at least one of {⁵⁷La, ⁵⁸Ce, ⁵⁹Pr,⁶⁰Nd, ⁶¹Pm, ⁶²Sm, ⁶³Eu, ⁶⁴Gd, ⁶⁵Tb, ⁶⁶Dy, ⁶⁷Ho, ⁶⁸Er, ⁶⁹Tm, ⁷⁰Yb and⁷¹Lu}, also known as the lanthanide series. For purposes of the instantinvention, yttrium, ³⁹Y, is considered a rare-earth metal and consideredincluded when [RE] is used. Furthermore, it is also disclosed rare-earthoxide based compounds containing Ge can also be utilized, such as,rare-earth alumino-germanate, (RE_(x)Al_(y)Ge_(z)O_(w)).

Furthermore, optionally, a barrier layer is chosen to function as aninsulator and/or dielectric. For thin film solar cell and TFT using SoG,the insulating nature of a substrate is advantageous for electricalisolation of devices on the SoG substrate. Therefore, the function ofthe barrier layer and/or a substrate may function as insulators and/ordielectrics, alternatively or simultaneously. An added advantage ofusing rare-earth oxide barrier layer in silicon-on-glass is theselective silicon etch stop provided by the different chemistry of arare-earth compound versus a glass substrate. Another example solar cellalternate embodiment is the use of barrier layer in SoG article withproperties of: (i) transparent to a substantial portion of the solarspectrum with high energy absorption edge greater than or equal to 3 eV;(ii) electrically conductive; and (iii) provide resistance to transportof alkali ions. The barrier layer with the aforementioned properties mayact as an optically transparent and electrically conducting layer andprovide barrier to alkali transport across said barrier layer. Thisburied transparent conductive barrier layer (TCBL) can be used to form acontact layer for vertical p-i-n and/or p-n junction solar cells formedon the SoG article.

The drift of alkali ions through SiO₂ in a MIS (where M=Al, I=SiO₂ andS=Si) structure is asymmetrical, where the activation energy for driftfrom the metal-SiO₂ interface is larger than that from the Si—SiO₂interface. Traps at the metal-SiO₂ interface exhibit a deeper energycompared to the Si—SiO₂ interface, thereby making emission moredifficult at the former. The asymmetry is not present in poly-Si gatecontact MOS devices. The motion of sodium ions in particular, aregoverned by emission of ions from traps at the interface and subsequentdrift through the oxide. The mobility of alkali metals is given by theexpression μ=μ_(o)exp(−E_(A)/kT). Typical parameters for Sodium:μ_(o)(Na⁺)=3.5×10⁻⁴ cm²/V.s, E_(A)(Na⁺)˜0.44; Potassium:μ_(o)(K⁺)=2.5×10⁻⁴ cm²/V.s, E_(A)(K⁺)˜1.04; and Lithium:μ_(o)(Li⁺)=4.5×10⁻³ cm²/V.s, E_(A)(Na⁺)˜0.47. In comparison, Copperexhibits μ_(o)(Cu²⁺)=4.8×10⁻⁷ cm²/V.s, E_(A)(Cu²⁺)˜0.93.

FIG. 1A depicts schematically the physical MOS layer structure formed ona SoG substrate comprising a thin film semiconductor 102 in intimatecontact with a high sodium ion concentration glass substrate 101, suchas (Na₂O)_(x)(SiO₂)_(y) glass. A further dielectric oxide 103 andpolycrystalline semiconductor gate contact 104 followed by a metal gateelectrode 105 form a general gate stack.

FIG. 1B depicts the energy band structure of the MOS SoG device as afunction of cross-sectional distance vertically through the layers. Thehigh concentration of sodium ions 106 within the glass substrate 101 arefree to migrate 109 across interfacial boundaries into the semiconductorthin film 102, oxide layer 103 and polycrystalline semiconductor layer104. For the present example in FIG. 1B, the band energy alignments areshown for thin film semiconductor chosen from single crystal Si, theoxide 103=SiO₂, layer 104=poly-Silicon and metal contact 105 M=Aluminum.If the MOS SoG structure is illuminated by 3.5-5 eV ultraviolet photons,electrons from the conduction (107) and valence (108) band of Si may beinjected into the SiO₂ conduction band (CB). These UV generated andinjected electrons may be capable of passivating and/or neutralizing theNa⁺ ions residing at the metal-SiO₂ and Si—SiO₂ interfaces.Nevertheless, it is disclosed the large concentration of alkali ionssourced from the glass substrate deleteriously degrade the performance,long term stability and reliability of the MOS SoG device. Possibleprior art solutions are: (i) the use of multi-alkali effect in alkalisilicate glasses, which can be used to significantly reduce ionicconductivity; or (ii) Alumino-borosilicate glasses, which may act assinks for sodium and other process impurities.

The present invention discloses a solution to the problem of alkalicontamination of the thin film semiconductor active layer via the use ofbarrier layer as is shown in the modified MOS SoG structure of FIG. 2.The alkali-silicate glass 101 of FIG. 2A depicts sodium ions 106 blockedfrom migrating beyond the alkali barrier layer 200. The barrier layer200 is disposed substantially between the thin film semiconductor layer102 and the glass substrate 101. Silicon dioxide has a band gap energyof E_(g)(SiO₂)˜8.8 eV and the barrier layer 200 has a band gap ofE_(BL)<E_(g)(SiO₂). FIG. 2B, shows a further criteria for the alkalibarrier layer which is the advantageous partitioning of the valence(ΔE_(v)) and conduction (ΔE_(c)) band offsets relative to the thin filmsemiconductor conduction band (CB) and valence band (VB) extrema.

A simple yet instructive model of a two component sodium-silicate glass(Na₂O).(SiO₂)=Na₂SiO₃ is now described to aid but not limit the utilityof engineering sodium-ion barrier layer(s) in SoG article. For example,the range of glass formation in the Na₂O—SiO₂ system is continuous fromSiO₂ up to the meta-silicate composition Na₂SiO₃, which does not readilyform a glass phase. Silica is a continuous network of SiO₄ tetrahedra.The introduction of Na₂O into SiO₂ results in the formation ofsingly-bonded or non-bridging oxygen atoms, where the oxygen atoms arelinked to only one Si atom. That is, not all oxygen atoms are bonded totwo silicon atoms as in the SiO₄ network. Sodium ions are linked tosurrounding oxygen atoms via ionic bonds that are much weaker than Si—Obonds. The extra oxygen atoms supplied by the Na₂O increases theoxygen-to-silicon ratio O:Si>2. Therefore, sodium silicate glass isstructurally weaker than pure vitreous silica (SiO₂). Increasing theNa₂O content causes a greater number of non-bridging oxygens to beformed, until the material phase segregates into isolated SiO₄tetrahedra linked together by ionic Na—O bonds.

By way of example and not intended to be limited to any particulartheory, is the use of rare-earth compounds, such as rare-earth oxides(REOx), as barrier layer. REOx compositions exhibit approximately,eqi-partition conduction band offset ΔE_(c)˜2.4 eV relative to singlecrystal Si. Binary rare-earth oxides with the pyrochlore and bixbyitecrystal structures are vacancy-ordered derivatives of the CaF₂-typefluorite structure and exhibit lattice parameters approximately twicethat of Si. Therefore, a close lattice match with Si and other elementaland/or compound semiconductors can be achieved by combinations ofvarious rare-earth compounds such as metal oxides. Defects, such asmisfit dislocations, at the Si/rare-earth oxide dielectric interfaceinfluence the mobility of charge carriers in the underlyingsemiconductor layer. Extended defects in bixbyite/Silicon epitaxy suchas REOx films grown on Si(111) and Si(001) may also be usedadvantageously in the present invention for electrical conductivityoptimization. The REOx bixbyite structure can be described as a vacancyordered fluorite with two oxygen vacancies per fluorite unit cell,causing the bixbyite unit cell parameter to be twice that of fluorite inall three dimensions. Atomic and molecular interstitial defects andoxygen vacancies in single crystal rare-earth oxide (REOx) can also beadvantageously engineered via non-stoichiometric growth conditions. Theatomic structure of singly and doubly positively charged oxygenvacancies (O_(v) ⁺, O_(v) ²⁺), and singly and doubly negatively chargedinterstitial oxygen atoms (O_(i) ⁻, O_(i) ²⁻) and molecules (O_(2i) ⁻,O_(2i) ²⁻) can be engineered in defective single crystals ofREO_(x=1.5±y), 0≦y≦1). Rare-earth metal ion vacancies and substitutionalspecies may also occur and an oxygen vacancy paired with substitutionalrare-earth atom may also occur. However, atomic oxygen incorporation isgenerally energetically favored over molecular incorporation, withcharged defect species being more stable than neutral species whenelectrons are available from the rare-earth conduction band. It isdisclosed that oxygen vacancies advantageously inhibit alkali iontransport and thus can be used as a component of an effective barrierlayer. It is disclosed in the present invention that oxygen vacanciescan be used as part of a rare-earth based compound as an effectivebarrier to positive ion migration, and more preferably inhibit Na⁺ ions.

Optional barrier layer materials are, for example, rare-earth nitride(REN), rare-earth oxynitride (REO_(x)N_(y)), rare-earth phosphide (REP),rare-earth oxyphosphide (REO_(x)P_(y)), rare-earth carbide (REC_(y)),rare-earth oxycarbide (REO_(x)C_(y)), aluminium rare-earth oxide(RE_(x)Al_(y)O_(w)), and rare-earth aluminosilicate(RE_(x)Al_(y)Si_(z)O_(w)), aluminium oxide (Al₂O₃), silicon nitride(SiN_(x)), silicon-aluminium-nitride (Si_(x)Al_(y)N_(z)), phosphateglass, P₅O₅, borophosphate silicate glass BPSG, and combinations andnon-stoichiometric combinations thereof.

Chlorine may also be used to inhibit sodium ion transport in silica.Therefore, a chlorinated surface of silicate glass is also a possiblealkali diffusion barrier; optionally a barrier layer high in freechlorine in combination with a rare-earth composition is disclosed.

FIG. 3 describes the geometry used for ion implantation of foreignspecies 301 into preferentially CZ Si substrate 304 to form a Gaussianprofile distribution volume 302 of said ions in the Si crystal. Thedefect plane 303 substantially plane parallel to the Si crystal surface.The depth of the peak of the defect layer distribution residing adistance L_(D) from the Si surface. An optional protective oxide layerand/or alkali barrier layer, 306 is also shown.

FIG. 4 shows calculated depth profiles for H+ ions 401 using variousincident energy implants. In preference the ion species is chosen fromhydrogen and/or helium. For the case of Fr, the peak depth L_(D) versusimplant energy range 100 keV≦E≦5 MeV is shown. Clearly, the defect layerdepth beneath the surface can be placed in the range 1≦L_(D)<250 μm,depending on the energy used. The calculated results were performedusing SRIM 2003 ion implant code, and L_(ox)=200 Å SiO₂. FIG. 5 showsexemplary ion implantation into an original device substrate. FIG. 6shows exemplary ion implantation into an original device substrate.

FIG. 7 shows the distribution of Fr ions 701 in the buried layer beneaththe Si surface for the case of 3 MeV.

In one embodiment a process is used to fabricate a vertical typeopto-electronic solar spectrum energy conversion device using thin filmsingle crystal semiconductor layer transfer method. In preference thesemiconductor is chosen from silicon or germanium or combinationsthereof, an alternative substrate is chosen from silicate glasscompositions, and more preferably alkali-silicate glasses. The alkalibarrier layer is chosen according to the specifications disclosed in thepresent invention.

FIG. 8 shows individual parallel process paths for fabrication of thinfilm single crystal solar cell on glass article. A single crystal CZ Sisubstrate 801 and alternative substrate 807 are cleaned and prepared forprocessing. An optional SiO₂ protective layer 802 is deposited orthermally grown on the CZ Si substrate 801. A barrier layer may also bedeposited upon or in place of layer 802. The CZ substrate is thenimplanted according to the method described in the present invention toform a buried defect layer 804. A cleaned alternative substrate 807 isthen deposited with a uniform barrier layer 808.

Alternative substrate 807 is preferably chosen from alkali-silicateglass. FIG. 9 shows how the alternative substrate with insulating and/orconductive barrier layer 809 and implanted CZ Si substrate 806 arejoined together 810 with opposing surfaces 850 and 860. The surfacesmust be free from particulate contamination and can be vacuum joined,van der Waals or anodic and the like bonded together. FIG. 10 shows howa compound multilayer article 811 is then subjected to thermal annealingsequence 813 to strengthen the bond between surfaces 850 and 860 and toinitiate temperature dependent defect fracture 814 confined to a regionadvantageously aligned with CZ Si crystallographic axes. A thermalanneal sequence 813 generates fracture within said CZ Si crystalconfined substantially to the plane defined by the defect plane.

FIG. 11 next shows how, with application of external mechanical stimulus815 to at least one region of the edge of the compound article 811, thefracture propagates throughout the defect plane causing physicalseparation of remaining bulk CZ Si substrate 816 and thin film CZ Sicoupled to alternative substrate 817. The resulting defect plane mayexhibit rough surface 818 on both the exposed thin film CZ Si and thecleaved surface of the bulk substrate. The surface roughness of 818 mayhave surface features ranging from several nanometers to severalmicrometers depending on the 0:H ratio and implant energy. Typically,higher implant energies result in wider full width at half maximum ofthe Gaussian defect layer. For example, a 3 MeV Fr implant results in astraddle of ˜1 μm.

FIG. 12 shows how the wafer bonded thin film CZ Si and thus formedburied barrier layer on the glass substrate 817 are then processed toform a vertical type MIS, p-n junction and/or p-i-n diode solar celldevice 832. The vertical solar cell functions by converting incidentsolar radiation coupled into the thin film semiconductor layers 833 intophoto-generated electronic charge carriers. The incident solar radiationis directed in a vector initially incident upon the glass substratesurface, through the glass substrate and into the thin film absorberregion. Example solar cell devices are disclosed in the next section.Further, thin film semiconductor and/or dielectric and/or metalliclayers may be directly deposited upon surface 818 of SoG article 817.Thin film single crystal semiconductor layer 819 is suitable for directepitaxy of further single crystal semiconductors and dielectrics. Forexample, the initial bulk Si substrate 801 may be chosen as p-type Si(p:Si). The completed SoG article is therefore a single crystal p:Sithin film on glass article. A p-i-n diode structure can be formed fromthe p:Si SoG by further deposition of not-intentionally-doped intrinsicSi layer 830, followed by a n-doped Si layer 831. The p-i-n Sihomojunction diode 833 is suitable for solar cell devices.

FIG. 13 discloses an example method and general process flow forfabricating multiple single crystalline semiconductor layers 1312 upon abulk single crystal semiconductor substrate 1301. The multi-layersemiconductor stack 1312 is separated by ion-implantation technique 1306as described previously by a defect layer 1308.

Implanted ion species are chosen in preference from H⁺ and/or He⁺ ions.FIGS. 5 and 6 show exemplary ion implantation into an original devicesubstrate. Alternatively, methods disclosed in U.S. application Ser. No.11/788,153 are incorporated herein in their entirety by reference; theinstant invention discloses the addition of a rare-earth based barrierlayer in combination with previously disclosed semiconductor and/orsolar cell structures.

An example layer sequence 1312 is composed of: p-type Si substrate 1301;intrinsic Si (1302); n-type Si 1303; intrinsic Si 1304; p-type Si 1305.Upon wafer bonding onto glass substrate 809, as shown in FIG. 14, aremaining portion of thin film Si 1311 is separated from the bulk of theSi substrate 1301 via defect layer 1308.

FIG. 15 shows the transferred layer stack 1312 forming a p-i-n-i-p dopedSi multilayer diode coupled to the glass substrate 809. The structuremultilayer single crystal Si SoG device 1520 is suitable for solar celloperation by coupling solar radiation 1530 through the transparentsubstrate 807 and barrier layer 808 into the active region(s) comprising1312. The final surface 1510 defined by the defect plane can bemetallized to form an optical reflector and/or electrical contact(s).

FIG. 16A shows a general solar power spectrum 1601, punctuated withmultiple absorption regions. The peak spectral variance 1606 occurs atλ˜496 nm (˜2.5 eV) in the 400<λ≦600 nm region. Prior art opticalphoton-to-electron conversion devices employing semiconductors are wellknown. FIG. 16A shows the absorption coefficient α_(abs) 1604 of singlecrystal silicon (Si) 1603 and germanium (Ge) 1602 semiconductors. Theindirect bandgap semiconductors Si and Ge span major portions of thesolar spectrum. Close to the energy band gap, both Si and Ge have longwavelength absorption tails due to the indirect energy-momentum bandstructure. Looking closely at the absorption coefficient of Si in FIG.16A, it is shown that the absorption depth near the fundament band gapenergy (E_(g)(Si)=1.1 eV) is extremely long. This means that photonswith energy equal to or slightly greater than band gap energyE_(g)(Si)≧1.1 eV will penetrate a depth L_(e)=1/α_(abs), deep within thecrystal. That is, for 900<λ<1120 nm the penetration depth for 1/eabsorption (L_(1/e)) is 10<L_(1/e)<1000 μm, thus requiring thick Sisubstrates for bulk band edge solar cells. Not well known by researchersin the field, is the fact, that Si possesses one of the highest knownabsorption coefficient for all commercially mature semiconductors in theblue to UV region, λ˜<450 nm.

FIG. 16A also shows the overlap of Ge 1602 absorption with the solarspectrum 1601 as a function of wavelength 1605. Ge exhibits 10-100×higher absorption co-efficient than Si in the 1.1-3 eV range. This means10-100× thinner film absorbers using Ge are possible compared to Si. Theuse of Ge extends absorption down to 0.66 eV and therefore canpotentially access more of the available solar spectrum and availablepower. For the case of high volume, large area and low cost solar cellfabrication, large Si substrates (φ_(max)=450 mm diam., CZ growth) arestill advantageous and at least ˜10-50× cheaper than Ge substrates(φ_(max)=150 mm, CZ growth).

It is an aspect of the present invention to fully utilize the uniqueoptical and electronic properties of single crystal Si to form new typesof high efficiency solar cell devices. Furthermore, the utility and coststructure of wafer bonding is severely limited in available singlecrystal bulk substrate diameters if anything other than Si is used.

In theory, Si should be a very efficient solar cell material; howeverhigh energy photons degrade the conversion efficiency. FIG. 16B showsthe energy band structure of bulk single crystal Si as a function ofenergy 1650 and wave-vector 1651. The periodic array and definitesymmetry of Si atoms in the crystal forms an extended band structureconsisting of conduction (CB) 1652 and valence (VB) 1653 bands.Electrons and holes are constrained to satisfy the E-k dispersion, asshown. Silicon exhibits a complex band structure due to the diamond-likecrystal lattice, with critical point energy gaps E_(G)=1.1 eV,E_(Γ1)=3.4 eV, E_(Γ2)=4.2 eV, E_(X)=1.2 eV, E_(L)=2.0 eV, E_(L)=44 meV.The unstrained bulk valence band is composed of a heavy- (HH) andlight-hole (LH) band, degenerate at zone center k=0. The fundamental andindirect band gap E_(G), requires phonon participation for creating anelectron-hole pair via absorption of a photon with energy (E_(γ))co-incident with E_(G). Referring to FIG. 16B, Si also possesses directenergy band gaps between E_(Γ1) and E_(Γ2), resulting in very highabsorption co-efficients (refer short wavelength portion of FIG. 16A).High energy blue and UV photons are efficiently absorbed (within 0.11 μmof the surface for 400 nm photons, refer FIG. 16A) in the upperconduction and valence bands creating hot electron hole pairs with largeexcess energy relative to the fundamental edges at E_(G). These hotcarriers couple to the lattice and quickly thermalize or equilibrate byemitting lattice phonons of energy ω_(LO). The UV photogeneratedcarriers therefore cannot easily participate in photocurrent generationin bulk and/or thick Si p-n SJ devices relying on large carrier transitdistances. It is an object of the present invention to design highenergy photon absorption Si solar cell capable of extracting theenergetic photogenerated carriers.

In order to increase UV responsivity in Si, it is necessary to avoiddead layer formation on the irradiated Si surface. A method tocircumvent dead layer region formation is via creating a chargeinversion layer at the interface between a dielectric material andsemiconductor, for example the SiO₂/Si interface. Alternatively, aninversion layer can be generated by a potential energy Schottky barriervia appropriate work function metal placed in contact with intrinsic Si.The UV response of the inversion layer is superior to vertical and/orplanar p-n and/or p-i-n junction type photodiodes. Photovoltaicoperation can be optimized via a built-in voltage generated byadvantageous placement of a lightly doped junction formed close to thesurface of the device. High quality SiO₂ has a large band gapEg(SiO₂)˜8.8 eV, and does not absorb high energy solar UV light.Depending on the growth and/or deposition technique used to form SiO₂,the optical properties can be modified. Using gas source deposition,various amounts of hydrogen may be incorporated in the amorphous oxidelayer. The hydrogen may affect the transmission/absorption properties ofthe film. Conversely, SiO₂ and hydrogen are beneficial for surfacepassivation of the Si surface states which is a desirable property.

Thermally grown SiO₂ via oxidation and thus consumption of Si producesthe highest quality oxide and Si/SiO₂ hetero-interface. The bandalignment for the poly-Si gate contact MOS device using the Si/SiO₂system is shown in FIG. 1B. The energy difference between the Si CB andthe SiO₂ CB is ΔE_(c)˜3.1 eV. Similarly, the energy difference betweenthe Si VB and SiO₂ CB is ˜4.2 eV. Higher energy photons with energy inexcess of 3.1-4.2 eV are therefore capable of injecting electrons fromSi into the oxide. This effect can be used advantageously in devicesdisclosed herein.

Typically, SiO₂ is an optimal antireflection (AR) coating as well as apassivation layer. Transparent low loss AR layers are used in thepresent invention. Typically, wide band gap energy materials opticallytransparent to the solar spectrum, such as, SiO₂, Aluminium-oxide(Al₂O₃) magnesium-oxide (MgO), calcium fluoride (CaF₂), magnesiumfluoride (MgF₂), silicon-nitride (Si₃N₄), titanium-dioxide TiO₂,tantalum-pentoxide (Ta₂O₅) and the like are used. The present inventionfurther teaches a new class of wide band gap optical materials suitablefor optical coating, specifically, the materials of rare-earth metaloxide (REO_(x)), rare-earth metal oxynitride (REO_(x)N_(y)) andrare-earth metal oxy-phosphide (REO_(x)P_(y)), and combinations thereof,glasses and/or crystalline material. A rare-earth metal is chosen fromthe group commonly known as the lanthanide series. Mixtures includingSi, Ge, C, combinations of rare-earths and/or silicates can also be usedwith the aforementioned rare-earth based materials. An optical coatingmay comprise one or more layers wherein at least one layer comprises atleast one compound chosen from a group comprising:[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >0. Acoating layer may be single crystalline; optionally it may bepolycrystalline; optionally it may be amorphous; optionally opticalcoating material may comprise one or more layers, at least one of whichis single crystal.

A metal-insulator-semiconductor (MIS) device fabricated upon a glasssubstrate is disclosed in FIGS. 17A & 17B. The thin film single crystalsemiconductor layer 1703 is fabricated upon a transparent substrate 1701according to the methods of the present invention. Layer 1703 withthickness 1711 is chosen from single crystal Si, and the substrate 1701with thickness 1713 is chosen from low cost alkali-silicate glass. Analkali barrier layer 1702 with thickness 1714 separates the thin filmsemiconductor 1703 from the glass substrate 1701 in order to preventalkali ion contamination.

The SoG substrate is fabricated into the MIS device via optionalselective oxidation of thin film Si layer 1703 into SiO₂ regions 1704and/or 1705. Layer 1705 is a dielectric and/or insulating material andcan be chosen from SiO₂, SiN_(x) or single crystal rare-earth oxidecompositions as disclosed in U.S. Pat. No. 7,199,015, titled “Rare-earthoxides, nitrides, phosphides and ternary alloys with Silicon”. Theinsulating layer 1705 is preferably grown thin to act as a tunnelbarrier, although thick layers can also be used. The metal or conductivecontact layer 1706 collects photo-created carriers generated in theactive layer 1703 and in a region proximate to the Si/insulatorinterface. Electrical contacts to the active layer 1707 complete thecircuit. Incident optical radiation 1720 enters the glass substrate andis absorbed in the thin film Si layer 1703. Photons that are notabsorbed on first pass through 1703 are reflected by the oxide electrode1706, thereby enabling a second pass 1721 through the active layer 1703.This constitutes a 2-sun solar cell device. The MIS SoG equivalentcircuit is shown in FIG. 17B. Electrical contacts 1707 are equivalent.Metallization chosen for contacts may be different for the purpose oflow ohmic contact 1707 to 1703 and/or specific work function metal forthe oxide contact 1706. An optional AR coating 1730 can be depositedupon the glass substrate 1701 to minimize reflection losses 1722. The ARcoating may consist of multiple layers composed of transparent anddifferent refractive index materials.

Another embodiment of a MIS SoG solar cell device is disclosed in FIGS.18A & 18B. The devices are fabricated in a similar fashion to thedescription of FIG. 17A, however, multiple lateral devices are showninterconnects via a common active layer contact 1707. The MIS repeatingunit is laterally disposed across the SoG substrate on unit dimension1810. The distance between the electrodes 1707 & 1707 is shown as 1820.The electrode dimensions and spacing are chosen to optimize the cellefficiency and is dependent upon the materials used. It is disclosed theactive layer is continuously optically active and does not suffer deadlayers due to opaque electrodes impeding the coupling of opticalradiation into the active thin film 1703.

The multiple MIS SoG equivalent circuit is shown in FIG. 18B. Contacts1707 can be grouped and connected together forming an electrode suitablefor the extraction of photocurrent. Similarly, electrodes 1706 can alsobe connected together, thus forming multiple parallel connected MIS SoGdevices. That is, grouped contacts 1706 and 1707 form an external twoelectrical terminal module composed of parallel interconnected MISdevices. Alternately, series connected devices can be fabricated viasuitable electrical isolation of the thin film semiconductor.

Another embodiment of the present invention is the use of multilayersemiconductor structures disposed upon the glass substrate. Anotherembodiment is the use of single crystal semiconductor layers to form theactive regions. Yet another embodiment is the use of Si layers chosenfrom not-intentionally doped (i.e., substantially intrinsic, i), n-type(n) and p-type (p) doping. For solar energy conversion devices, layeredSi devices of the form of p-n and p-i-n diodes are efficientoptoelectronic conversion structures. An example p-i-n SoG embodiment isshown in FIG. 19A. The fabrication of the p-i-n SoG structure ispossible using the methods disclosed in the present invention. It isunderstood that p-n junctions and more complex structures are alsopossible. The glass substrate 1701 is separated from the single crystalthin film semiconductor 1902 layer via a barrier layer 1702 according tothe methods disclosed.

The p-i-n layer structure is composed of p-type Si (p:Si) 1902,intrinsic Si (i:Si) layer 1903, and n-type Si (n:Si) layer 1904. Layers1903 and/or 1904 can be deposited upon an initial SoG article comprisingn:Si on glass. Alternatively, the p-i-n structure can be initiallydeposited upon the single crystal p:Si substrate prior to wafer bondingand implant induced layer separation. Lateral oxidation of layer 1902may be used for lateral electrical isolation of devices disposed acrossthe SoG substrate via regions 1901. Passivation and/or environmentalsealing of the Si epi-layers is via layer 1905 and may consist of SiO₂and SiN_(x). Electrical contacts formed by 1906 to the n-type layer 1904and 1908 to p-type layer 1908 may not be the same composition. For,example, ohmic contacts to the different conductivity type layers mayrequire different metals. The active area useful for photocurrentgeneration is defined by the i-layer width 1907 of thickness 1923.Optical radiation is coupled in from the glass substrate 1720 into thepin device. The contact 1906 defines a reflective surface that enablesregeneration of photons such that another pass through the i-region mayoccur. This constitutes a 2-sun concentrator p-i-n solar cell fabricatedin a SoG structure. The equivalent circuit is shown in FIG. 19B, and isrepresented by a p-i-n diode 1920.

Multiple lateral p-i-n devices can be fabricated across the SoGsubstrate as shown in FIG. 20A. Utility of the highly resistive glasssubstrate and/or barrier layer is for the purpose of electricalisolation via lateral oxidation and/or etching.

Regions 1901 electrically isolate devices formed on layer 1902. Themetallization (M) and/or electrical contacts 2010 shows seriesinterconnection of p-i-n device forming the string p-i-n-M-p-i-n-M-p-i-n. . . . Optical radiation incident 1720 upon the glass substrate 1701 iscoupled through the transparent barrier layer 1702 into the i:Si 1903layers and reflected off the contacts 2010, thereby forming the 2-sunconcentrator structure. Passivation and/or environmental sealing of thep-i-n devices is via coating 2015. The equivalent circuit is shown inFIG. 20B where p-i-n devices 1920 are series connected. Photocurrentgenerated within each device flows through interconnects 2010 therebyforming two terminal external module.

The absorption co-efficient as function of wavelength for the thin filmsemiconductor layer can be used for selecting the thickness andwavelength region operation. In particular, Si exhibits a highlynon-linear absorption character as a function of optical wavelengths.Referring to FIG. 16A, it can be seen α_(abs)(λ) in Si varies by almostfive orders of magnitude in the range 350≦λ≦1127 nm. Short wavelengthphotons are therefore absorbed in a very short distance compared to longwavelength photons in the vicinity of the indirect band gap E_(G).

FIG. 22A discloses a stacked layer structure consisting of two p-i-ndiodes comprising different intrinsic absorber thicknesses. Inpreference, the semiconductor is selected from single crystal Si and thesubstrate from alkaline-silicate glass. An example embodiment disclosesa first p-i-n diode comprising p:Si layer 2204, i:Si layer 2205 and n:Silayer 2206. A second p-i-n diode formed upon the first diode comprisingp:Si layer 2207, i:Si layer 2208, and n:Si layer 2209. This sequenceforms the p-i-n-p-i-n stacked diode. Alternately, the sequencen-i-p-n-i-p can also be formed. Yet another embodiment uses the layersequences p-i-n-i-p or n-i-p-i-n. Regardless, the NID i-regions aregrown with different thickness, L_(s) 2301 and L_(L) 2311, such that thethinner region is positioned closest to the glass substrate. Theelectrical contact layers 2211 and 2212 are formed on the first and lastlayers comprising the stacked diodes. Incident short wavelength opticalradiation λ_(s) enters the glass substrate 2201 and is preferentiallyabsorbed in the first thin i:Si layer 2205 and/or p-i-n diode.Similarly, long wavelength optical radiation λ_(L) enters the glasssubstrate 2202 and is preferentially absorbed in the second thick i:Silayer 2208 and/or p-i-n diode.

FIG. 22B shows the generation rate G(λ, z) 2225 of electron-hole pairsas a function of vertical distance, z 2220, through the layeredstructure.

Short wavelengths in Si exhibit very large absorption co-efficient (100μm⁻¹ @ λ_(s)=400 nm) and thus the first i:Si region 2205 can be madethin (L_(L)˜0.01 μm). Similarly, long wavelength photons co-incidentwith the band edge E_(G) exhibit relatively low absorption co-efficientand thus can be made thick 0.01 μm⁻¹ @ λ_(s)=1000 nm, L_(L)˜100 μm).

FIGS. 23A & 23B further show wavelength bands 2300 & 2310 used for, asan example, tandem Si: p-i-n-p-i-n solar cells. The theoreticalefficiency of the proposed tandem cell is equivalent to a two-junctionsolar cell, and thus in excess of the SJ limit=25%. It is important tonote that the disclosed two-junction device uses only Si semiconductormaterials in the layer stack. This technique works particular well forSi compared to Ge due to the large non-linearity in absorptionco-efficient of Si as a function of wavelength and advantageous overlapwith the solar spectrum.

Another embodiment utilizes a hybrid device based on incorporating theadvantageous features of MIS and PIN solar cell devices. FIG. 24discloses a MIS/PIN hybrid wherein the MIS section 2420 is used as theshort wavelength converter and the PIN device 2430 is used as the longerwavelength converter. In preference, the semiconductors forming thestacked layers are single crystal and/or polycrystalline and/oramorphous structure. The insulator 2402 layer may be chosen fromamorphous SiO₂ and/or single crystal rare-earth based materials, such asrare-earth oxide and oxynitride (REO_(x) or REO_(x)N_(y)). If insulator2402 is amorphous then thin film semiconductor layer 2400 may be chosenfrom polycrystalline and/or amorphous structures using the wafer bondingtechnique disclosed herein. Alternately, multiple wafer bonding stepsmay be used to form single crystal layers 2400, 2403, 2402 and 2405prior to lamination with glass substrate 1701. If the insulator 2402 ischosen from substantially single crystal compositions (e.g.; rare-earthoxide and like), then epitaxial Si may be deposited directly upon 1402,thereby forming a single crystal epitaxial growth sequence according tothe method disclosed in the present invention.

Referring to FIG. 24, an example embodiment of the MIS/PIN hybrid is viathe following layer sequence: alkali silicate glass substrate 1701;alkali barrier layer 1702; a first semiconductor layer p:Si 2400; ainsulator layer 2402; a n:Si layer 2403; a NID i:Si layer 2404; and ap:Si layer 2405. Electrodes 2406 and 2407 may be metallization tocontact layers 2405 and 2400, respectively. The layer sequence forms aMIS diode with silicon contact layer to the insulator. In fact, thep:Si/SiO₂/n:Si stack (i.e.; 2400/2402/2403) forms an inversion channelMOS structure suitable for high energy photon solar energy conversion.The following NIP (n:Si/i:Si/p:Si) structure is formed via the layersequence 2403/2404/2405. The intrinsic layer 2404 thickness is chosen toadvantageous absorb a portion of the solar spectrum that has not beendepleted by the MIS device.

Solar optical radiation is incident upon the glass substrate 1701 and iscoupled into the MIS/PIN hybrid via an optional transparent barrierlayer 1702.

The MIS device is preferentially made with a thin insulator 1402(5≦L_(ox)≦500 Angstroms) so as to allow tunneling of photo-createdcarriers in the active layer 2400. Referring to FIG. 2B, the possibilityUV generated hot electron injection from the CB and/or VB of Si into theCB of the insulator may also occur. Electrode 2406 can also beengineered to function as a back reflector allowing long wavelengthradiation not absorbed by the MIS section to be recycled back throughthe device. Therefore, the MIS/PIN hybrid solar cell fabricated on SoGalso form a two-junction and 2-sun solar concentrating device.

The present invention discloses a new manufacturing method of formingthin film and single crystal semiconductor layer(s) disposed upon glasssubstrates. Furthermore, a method using alkali barrier layers isdisclosed in order for low cost alkali-silicate glass to be used. Newsolar cell structures on glass or other inexpensive substrates areenabled by the disclosed methods. As used herein, alternatives to glasssubstrates may be used wherever glass has been given as an example;alternatives to glass include, but are not limited to, plastics,including polyimide and Kapton, flexible plastics, insulative coatedmetal, ceramic, recycled silicon wafers, silicon ribbon, poly-siliconwafers or substrates and other low cost substrates known to oneknowledgeable in the art.

Solar energy conversion devices disclosed using the thin filmsemiconductor SoG article are: (i) single absorber MIS, PIN devices;(ii) dual absorber PINIP, NIPIP, PINPIN, MIS/PIN hybrid. A unique aspectof disclosed solar cell devices is the recycling of photons that havenot been absorbed in a first pass through the device via a reflectiveback electrode. This constitutes a 2-sun concentrator structure,enabling increased efficiency beyond the single junction limit.

Yet another unique aspect of disclosed solar cell devices is thepreferential use of the non-linear absorption of silicon as a functionof wavelength in order to construct dual wavelength solar cell. Thisconstitutes a 2-junction device structure, enabling increased efficiencybeyond a single junction limit.

In one embodiment a device for converting radiation to electrical energycomprises an active layer for the converting radiation to electricalenergy, a barrier layer and, optionally, a replacement substrate,optionally with electrodes connecting to the active layer, wherein theactive layer, optionally, comprises one or more different rare-earthions and the barrier layer comprises at least one rare earth andseparates the active layer and the replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises an active layer for the converting radiation to electricalenergy; and a replacement substrate transparent to a majority, at least50%, of the radiation for converting. A device for converting radiationto electrical energy comprises, optionally, a replacement substrate; anactive layer for the converting radiation to electrical energycomprising at least one lateral p-i-n structure; optionally, the activelayer comprises one or more rare-earth ions and a barrier layercomprising at least one rare earth separating the active layer and thereplacement substrate.

An integrated device for converting radiation to electrical energycomprises a replacement substrate; one or more active layers for theconverting radiation to electrical energy comprising multiple devicesinterconnected such that there are a plurality of devices for supplyinga voltage interconnected; and a plurality of devices for supplying acurrent interconnected; optionally, the active layer comprises one ormore different rare-earth ions and a barrier layer comprising at leastone rare earth separating the active layer and the replacementsubstrate.

In one embodiment a device for converting radiation to electrical energycomprises a first portion of a first conductivity type at a first levelof doping; a second portion of first conductivity type at a second levelof doping less than the first, wherein a first drift voltage is imposedacross the second portion; a third portion of first conductivity type atabout the first level of doping; a fourth portion of first conductivitytype at about the second level of doping, wherein a second drift voltageis imposed across the fourth portion; a fifth portion of secondconductivity type at a third level of doping; such that the secondportion is a drift region and the fourth portion is an avalanche regionand electrons undergo avalanche multiplication in the avalanche regionbased upon the first drift voltage imposed across the second portion andthe second drift voltage imposed across the fourth portion; areplacement substrate; optionally at least one portion comprises one ormore rare-earth ions; alternatively, the first and second drift voltagesare set as a function of the energy of said radiation being converted;alternatively, at least said second and fourth portions comprise asemiconductor material comprising an indirect bandgap and a barrierlayer comprising at least one rare earth separating the active layer andthe replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises a first portion of a first conductivity type at a first levelof doping; a second portion of first conductivity type at a second levelof doping less than the first, wherein a drift voltage is imposed acrossthe second portion; a third portion of second conductivity type at athird level of doping; such that the second portion is a drift andavalanche region wherein electrons undergo avalanche multiplicationbased upon the drift voltage imposed across the second portion;alternatively, at least said second portion comprises a semiconductormaterial comprising an indirect bandgap; optionally, at least oneportion comprises one or more rare-earth ions; optionally said driftvoltage is set as a function of the energy of said radiation beingconverted; in some embodiments, at least about 50% of said electricalenergy is converted from radiation of wavelength 400 nm and shorter anda barrier layer comprising at least one rare earth separating the activelayer and the replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that alayer of the large band gap material are contacting a layer of the smallband gap material; and the large band gap material chosen from a groupcomprising rare-earth oxide (RE_(x)O_(z)), rare-earth germanium oxide(RE_(x)Ge_(y)O_(z)), rare-earth silicon oxide (RE_(x)Si_(y)O_(z)),rare-earth-silicon-oxide-phosphide (RE_(x)Si_(y)O_(z)P_(w)),rare-earth-silicon-oxide-nitride (RE_(x)Si_(y)O_(z)N_(w)),rare-earth-silicon-oxide-nitride-phosphide (RE_(x)Si_(y)O_(z)N_(w)P_(q))wherein X, Z>0 and Y, W. Q are ≧0; and a barrier layer comprising atleast one rare earth separating the active layer and the replacementsubstrate.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that theone or more layers of the large band gap material are contacting a layerof the small band gap material; and the large band gap material chosenfrom rare-earth germanium oxide (RE_(x)Ge_(y)O_(z)) and a barrier layercomprising at least one rare earth separating the active layer and anoptional replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises a substrate; one or more layers of a large band gap material;and one or more layers of a small band gap material for convertingradiation to electrical energy, such that the one or more layers of thelarge band gap material are contacting a layer of the small band gapmaterial; and the large band gap material chosen from rare-earth siliconoxide (RE_(x)Si_(y)O_(z)) and a barrier layer comprising at least onerare earth separating the active layer and the replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that theone or more layers of the large band gap material are contacting a layerof the small band gap material; and the large band gap material chosenfrom rare-earth-silicon-oxide-phosphide (RE_(x)Si_(y)O_(z)P_(w)) and abarrier layer comprising at least one rare earth separating the activelayer and an optional replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that theone or more layers of the large band gap material are contacting a layerof the small band gap material; and the large band gap material chosenfrom rare-earth-silicon-oxide-nitride (RE_(x)Si_(y)O_(z)N_(w)) and abarrier layer comprising at least one rare earth separating the activelayer and the replacement substrate.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that theone or more layers of the large band gap material are contacting a layerof the small band gap material; and the large band gap material chosenfrom rare-earth-silicon-oxide-nitride-phosphide(RE_(x)Si_(y)O_(z)N_(w)P_(q)) and a barrier layer comprising at leastone rare earth separating the active layer and the replacementsubstrate.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that theone or more layers of the large band gap material are contacting a layerof the small band gap material; and the small band gap material chosenfrom a group comprising rare-earth-silicon (RE_(x)Si_(y)),rare-earth-germanium (RE_(x)Ge_(y)), rare-earth-phosphide (RE_(x)P_(y)),rare-earth-nitride (RE_(x)N_(y)) such that the small band gap is lessthan about 3 eV and, optionally, a barrier layer comprising at least onerare earth separating the active layer and an optional replacementsubstrate. In alternative embodiments a small band gap may be less thanabout 2.5 eV; optionally, a small band gap may be less than about 2.0eV; optionally, a small band gap may be less than about 1.5 eV;optionally, a small band gap may be less than about 1.0 eV.

In one embodiment a device for converting radiation to electrical energycomprises, optionally, a replacement substrate; one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial for converting radiation to electrical energy, such that theone or more layers of the large band gap material are contacting a layerof the small band gap material; and the small band gap material chosenfrom rare-earth-germanium (RE_(x)Ge_(y)) and a barrier layer comprisingat least one rare earth separating the active layer and the replacementsubstrate. In one embodiment a device for converting radiation toelectrical energy comprises, optionally, a replacement substrate; one ormore layers of a large band gap material; and one or more layers of asmall band gap material for converting radiation to electrical energy,such that the one or more layers of the large band gap material arecontacting a layer of the small band gap material; and the narrow bandgap material chosen from rare-earth-phosphide (RE_(x)P_(y)) and abarrier layer comprising at least one rare earth separating the activelayer and the replacement substrate. In one embodiment a device forconverting radiation to electrical energy comprises, optionally, areplacement substrate; one or more layers of a large band gap material;and one or more layers of a small band gap material for convertingradiation to electrical energy, such that the one or more layers of thelarge band gap material are contacting a layer of the small band gapmaterial; and the narrow band gap material chosen fromrare-earth-nitride (RE_(x)N_(y)) and a barrier layer comprising at leastone rare earth separating the active layer and the replacementsubstrate.

As used herein a replacement or alternative substrate is optionally asubstrate chosen from a group comprising glass, float glass, quartz,alkali-silicate glass, plastics, including polyimide and Kapton,flexible plastics, insulative coated metal, ceramic, recycled siliconwafers, silicon ribbon, poly-silicon wafers or substrates and other lowcost substrates known to one knowledgeable in the art. A replacementsubstrate takes the place of an original substrate after the fabricationof an active layer upon an original substrate; by means of a “layertransfer process” an active layer is transferred from an originalsubstrate to a replacement substrate; additional processing may beperformed after the transfer to complete device fabrication.

As used herein an active layer comprises one or more layers ofsemiconducting, insulative and/or metallic materials sufficient toenable a solar cell or other thin film solid state device as disclosedherein. An “active layer” is fabricated originally on a substratedifferent than a replacement substrate; an active layer is transferredto a replacement substrate by a method disclosed herein or by referencedisclosed herein or by techniques known to one knowledgeable in the art.

In one embodiment a device for converting radiation to electrical energycomprises at least one single crystal Si thin film layer and one layercomprising a rare-earth in an active region and one layer comprising arare-earth in a barrier layer. In one embodiment a device for convertingradiation to electrical energy comprises a MIS device on SoG.

In one embodiment a device for converting radiation to electrical energycomprises a PIN device on SoG; alternatively a PINPIN dual diode on SoGusing different thickness i-regions to efficiently absorb differentportions of the solar spectrum is a device for converting radiation toelectrical energy; alternatively, a MIS/PIN hybrid device on SoG is adevice for converting radiation to electrical energy; alternatively, aSoG device with a barrier layer may be combined with one or more sunconcentrators.

In some embodiments a semiconductor device comprises a substrate, one ormore layers of a semiconductor device and a barrier layer comprising oneor more layers wherein at least one is chosen from a group comprisingrare-earth sesquioxide (RE2O3), rare-earth dioxide (REO2), rare-earthmonoxide (REO), rare-earth nitride (REN), rare-earth oxynitride(REOxNy), rare-earth phosphide (REP), rare-earth oxyphosphide (REOxPy),rare-earth carbide (RECy), rare-earth oxycarbide (REOxCy), aluminiumrare-earth oxide (RExAlyOw), rare-earth aluminosilicate (RExAlySizOw),rare-earth ternaries, such as, SiErN, SiErP, GeLAN, GeLaP, SiGeErn,SiGeErP, aluminium oxide (Al2O3), silicon nitride (SiNx), (SixAlyNz),Hf-oxide and HfON, Zr-oxide and ZrON, MgO and combinations thereof; insome embodiments a barrier layer and/or substrate may undergo a surfacetreatment such as a surface treatment of Al₂O₃ via nitridation, formingAlN interlayer, chlorination, phosphorization, and/or treatment with aboron compound.

FIG. 24A discloses process steps 1001 through 1009, required for theformation of thin film layer upon sacrificial layer and subsequentseparation. First, the parent substrate 1021 is cleaned and prepared forepitaxy. In one embodiment the substrate 1021 is chosen from singlecrystal silicon with (100)-, (111)- or (110)-oriented surface. Next, asubstantially single crystal sacrificial epitaxial layer 1022 isdeposited with predetermined thickness; thickness may range from 10 nmto 10 microns depending upon composition and process parameters. Thethin film semiconductor layer 1023 is directly deposited upon thesacrificial layer 1022. The thin film semiconductor layer is alsosubstantially single crystal and uniform in thickness. In oneembodiment, the sacrificial layer is chosen from a rare-earth basedcompound of the form RE_(x)O_(y)N_(z)P_(w); 0≦y, z, w≦5, 0<x≦5. A thinfilm semiconductor layer is chosen from silicon, germanium orsilicon-germanium alloy; Alternatively, a thin film semiconductor layeris chosen from Group IV, Group III-V, or Group II-VI materials orcombinations thereof. Alternatively, a semiconductor substrate, primaryor secondary is chosen from Group IV, Group III-V, or Group II-VImaterials or combinations thereof.

The completed composite single crystal article 1020 is then subjected toselective layer process 1024. FIG. 24B, Step 1005 schematically showsthe structural and/or chemical modification of selective process 1024 onthe sacrificial layer 1022. The region 1025 depicts the selectivemodification of layer 1022 into new form 1025. The lateral transportand/or diffusion and/or reaction of process 1024 results in region 1025extending into the interior of the composite article confined in aregion occupied by the initial layer 1022.

The lateral selective modification of the sacrificial layer 1022 iscontinued until the entirety of layer 1022 is modified, thereby formingnew uniform layer 1025. The parent substrate and thin film semiconductorlayer are substantially unaffected by process 1024. FIG. 24C depicts theremoval of layer 1022 and 1025 such that the thin film layer 1023 isphysically separated 1026 from the parent substrate 1021.

The result of process 1024 on layer 1022 may consume the constituentatoms comprising layer 1022 and be removed during processing.Alternately, layer 1022 may undergo a structural phase change due toprocess 1024, for example transform from single crystal structure toamorphous or porous or nanocrystalline or microcrystalline or powderform. Another selective removal process may be required to removeresultant layer or form 1025.

The utility of the aforementioned method is via parallel processing ofthin film article with an alternative substrate prior to thin film layerseparation.

FIGS. 25A, 25B, 25C and 3 disclose schematic processing steps requiredfor the formation of thin film semiconductor on alternative substrate.

First, the single crystal thin film 2023 and sacrificial layer 2022 aredeposited via direct epitaxy on parent substrate 2021. An optionalinterfacial bonding layer (IBL) 2024 with surface 2025 suitable forbonding to alternative substrate may be also deposited. The IBL does notneed to be single crystal and can be deposited ex-situ prior to waferbonding to alternative substrate 2027. The alternative substrate 2027 iscleaned and prepared 2005 with bonding surface 2026 optionally coatedwith layer 2028. Optionally, the alternative substrate coated with layer2028 may result in predetermined warpage of substrate 2027. Step 2007shows convex surface bowing due to predetermined film stress 2028 orconcave warpage in 2008. If alternative substrate is geometricallymodified by layer 2028, then surface 2032 or 2033 is used for intimatecontact with final exposed surface of 2023 or 2024.

For clarity, the following process steps are described withoutalternative substrate geometry modification. FIG. 25B schematicallydescribes the physical joining 2029 and subsequent bonding of surfaces2026 and 2025 forming composite article 2031 comprising parent substrate2021, sacrificial layer 2022, thin film semiconductor layer 2023, IBL2024 and alternative substrate 2027. The wafer bonding process isperformed such that the surfaces 2025 and 2026 when in contact are freefrom contamination, particulate and voids, forming a well defined andhomogeneous interface.

FIG. 25C schematically described the selective and lateral modificationof the sacrificial layer 2022 by process 2040. The initial process 2011is continued until the sacrificial layer is consumed and/or modified inentirety. The lateral process completing at the center of the compositearticle, thereby forming uniform region 2041 in step 2013. Other thanthe sacrificial layer 2022, all other layers and substrate aresubstantially unaffected by process 2040.

FIG. 26 schematically describes the possible layer separation paths. Theselective layer modification of 2022 into 2041 results in compositearticle 3000. Process 2040 or by the action of subsequent mechanical orchemical or reactive process provides a physical separation of the thinfilm semiconductor layer 2023 from the parent substrate 2021. The thinfilm semiconductor layer is bonded to alternative substrate. In oneembodiment, thin film semiconductor layer 2023 is chosen from singlecrystal silicon, germanium or silicon-germanium alloy; in alternativeembodiments a substrate may be chosen from a group comprising sapphire,silicon carbide, III-V compounds, and II-VI compounds. The parentsubstrate 2021 is chosen from single crystal silicon substrate. Thealternative substrate is chosen from amorphous material such as glass,Pyrex™, metal foil, metal substrate and/or flexible substrate. Processpaths 3001, 3002 and 3003 all result in thin film semiconductor onalternate substrate 2027. Process path 3001 shows residual sacrificiallayer 2041 can be substantially, completely separated from thin filmsemiconductor layer 2023 upon physical separation. Alternately, aportion of layer 2041 remains in contact with the surface of layer 2023,as shown in process path 3002.

FIG. 27 discloses an embodiment for sacrificial layer composition andthe possible selective process reactions for modification of thecomposition and crystallographic structure. The sacrificial layer iscomposed of rare-earth oxide (RE₂O₃ or REO₂ or generally RE_(y)O_(x),where 0<x, y≦5) and can be deposited in single crystal form on siliconor other substrates. By way of example, and not limited to, rare-earthoxide crystals readily undergo chemical reaction with hydrogen, waterand carbon-dioxide. Other reactions are also possible and areincorporated herein. For example, single crystal rare-earth oxide can behydrated 4007 by immersion of REO_(x) 4001 in water H₂O₍₁₎ and/orreacted with steam H₂O_((g)) 4004. Typically, single crystal REO_(x),x≈1.5, reacts with water to form hydrated clusters RE₂O_(x)(H₂O)_(y)thereby destroying the single crystal structure. Other reactions such ashydrogenation 4005 and carbonization 4006 are possible with reactantproducts shown. Hydrogenation 4005 by reacting REO_(x) 4001 withH_(2(g)) 4002 forms rare-earth hydroxyl compounds. Carbonization occursby reacting REO_(x) with gaseous carbon, forming rare-earth carbide oroxy-carbide compounds.

The processes of hydration 4007, hydrogenation 4005 and carbonization4006 of single crystal rare-earth oxide 4001 results in morphologicalchange in structure. For example, single crystal REOx can be transformedinto amorphous or polycrystalline granules with increase in volume. Thisprocess is advantageous for cleaving of composite article 3000 into atleast one of process paths 3001, 3002, and 3003.

An alternative method for layer separation using rare-earth oxidesacrificial layer is via use of inherent catalyst function, as shown inFIG. 28. Rare-earth oxide compound layer 5002 is deposited assacrificial layer as single crystal structure as described in thepresent invention. The REO_(x) can behave as a catalyst when reactedwith incident gaseous compounds R_(A) and R_(B) 5006 transforming inputgaseous species into a new compound R_(c) 5008 through catalytic actionof REO_(x) 5002 and consuming reactants R_(A) & R_(B) 5006. The singlecrystal sacrificial layer 5002 is not chemically consumed in thecatalytic reaction but the process does modify the crystal structurefrom homogeneous single crystal layer into non-uniform fragments of REOxregions 5009. For example, FIG. 29 shows the catalytic process ofreactants R_(A) & R_(B) 6003 transforming into byproduct R_(c) 6006 viacatalyst REOx 6002. The long range order of the REOx crystal structureis destroyed during the process forming disordered polycrystallineREO_(x) in the form of granules, micro-crystalline, nanocrystalline orpowder. That is, the REOx epitaxial layer 6002 is structurally destroyedor modified 6007 by action of the catalytic process 6003/6004/6005.

Rare-earth oxides crystallize as fluorite or bixbyite crystallographicstructures, depending upon the specific RE species chosen. Both fluorite(REO₂) and bixbyite (RE₂O₃) rare-earth oxide crystals exhibit defects,such as oxygen or metal vacancies or interstitials. Oxygen vacanciesallow the relatively free transport of oxygen and/or other atomic ordiatomic species or molecular species through the bulk of the REO_(x)crystal. For example, O, N, H, C, P, O₂, N₂O, H₂O, CO₂, H₂, P₂, PH₃,etc. may penetrate the single crystal REO_(x) structure. Furthermore,RE_(y)O_(x) single crystals may possess defects such as oxygen vacanciespreferentially aligned along crystallographic axes, allowing long rangetransport through the bulk of the crystal. This property is advantageousfor the present invention for use as layer separation mechanism.

Another example of sacrificial layer separation using rare-earth basedmaterial is via selective etching and/or removal of the sacrificiallayer 7002 via process gases or liquids or reagents or reactive species7003, as shown in FIG. 30. As the sacrificial layer is consumed 7004 byformation of reactants 7005 the layer 7002 is ultimately removed fromthe surface of the substrate 7001. This process is shown as step 1009 inFIG. 24C and results in the layer separation of thin film semiconductoronto alternative substrate.

The advantage of the present invention is that optimized growth of theinitial single crystal article can be accomplished independent of thealternative substrate. The single crystal article, for example 2031,comprising thin film semiconductor on single crystal rare-earth oxidelayer deposited upon parent substrate can be fabricated prior to waferbonding alternate substrate. The selective removal and/or modificationof the single crystal sacrificial layer can be performed at conditionssuitable for processing alternative substrate composite article. Thatis, a low thermal budget process such as steam hydration can be used toperform thin film layer separation.

In one embodiment, single crystal silicon substrates are utilized as theprimary or parent substrate. The substantially single crystalsacrificial layer is formed using the general compound ofrare-earth-oxygen-nitrogen-phosphorus-carbon of general chemical formulaRE_(x)O_(y)N_(z)P_(w)C_(v). Alternatively, thin film semiconductorlayers may be chosen from Si, Ge, or SiGe alloys, GaAs, GaN, InN, InP,SiC or alternative Group IV, Group III-V or Group II-VI semiconductors;alternatively, a semiconductor substrate, primary or secondary is chosenfrom Group IV, Group III-V, or Group II-VI materials or combinationsthereof.

Thin film semiconductor devices can be patterned laterally uponalternative substrate using selective area epitaxy of crystallinesacrificial layer and removal of the same. FIGS. 31, 32, 33 and 34describe the selective area thin film device manufacture on alternativesubstrate. FIG. 31 shows the selective area epitaxy of sacrificial layer8004 disposed upon single crystal parent substrate 8006. For example,the selective areas 8004 in step 8100 may be deposited and patterned byuse of a shadow mask 8002 position between the source material flux 8001and the parent substrate surface 8006. Step 8200 shows the thin filmcrystalline semiconductor 8011 blanket deposited 8010 upon the patternedparent substrate comprising selective areas of crystalline sacrificialregions 8004. The thin film semiconductor layer (not necessarily thesame composition as the parent substrate) is deposited with thicknesssubstantially comprising uniform crystalline structure and thickness inregions where direct epitaxy on sacrificial layer occurs.

For the case of homo-epitaxy of semiconductor upon parent substrate, thecrystal quality will also be high. The thin film semiconductor layerthickness 8012 is substantially the same for direct epitaxy on parentsubstrate and sacrificial layer surfaces. Generally, the sacrificiallayer thickness 8005 is thicker than the thin film semiconductor layerthickness 8012.

FIG. 32 step 8300 shows the wafer bonding 8013 of alternative substratesurface 8012 with regions formed by thin film semiconductor layersurface 8011 deposited upon sacrificial layer 8004. The joined article8200 in step 8400 comprises alternative substrate and selective areapatterned thin film regions with intentional voids between alternativesubstrate and thin film semiconductor regions deposited directly uponparent substrate. FIG. 33 step 8500 schematically depicts the selectivearea modification and or removal 8014 of the sacrificial layer 8004 viamaterial selective process 8015. Step 8600 results in physical layerseparation by virtue of sacrificial layer removal into desired selectivearea thin film semiconductor on alternative substrate article 9001 andremaining patterned parent substrate 9002.

The separated parent substrate containing patterned thin filmsemiconductor regions 9002 can be recycled directly for use in step8200, bypassing the need for step 8100.

FIG. 34 step 8700 shows the released completed thin film semiconductoron alternative substrate article comprising patterned thin filmsemiconductor region 8011. Regions 8011 may be single crystal orpolycrystal or combinations thereof. Step 8800 schematically showssubsequent processing to produce thin film electron or optoelectronicdevices 8016 disposed upon alternative substrate.

A multi-junction solar cell can be fabricated usingamorphous-crystalline (a-c) semiconductors via the present invention.However, the effective band gap of an amorphous semiconductor istypically larger relative to the single crystal semiconductor form.Hetero-junction formation between the same chemical compositionmaterials but dissimilar structural forms, such as amorphous and singlecrystalline semiconductor, offer improved optical response for solarcell device. For example, amorphous Si (a-Si) exhibits an effective bandgap of 1.5≦E_(g)(a-Si)≦2.0 eV, compared to crystalline Si (c-Si) withE_(g) (c-Si)=1.1 eV.

FIG. 35 shows processing steps for further deposition of thin filmsemiconductors upon the selective area patterned single crystal regionsformed on amorphous substrate 8012. For example, the alternativesubstrate is transparent to solar radiation and comprised of glass. Thethin film semiconductor 8011 is chosen from Si or Ge and formed usingthe sacrificial layer separation technique described herein.

Further epitaxy or deposition upon the article in step 9100 results innew thin film layers disposed upon amorphous substrate 8012 or singlecrystal semiconductor regions 8011, as shown in step 9200. For example,the thin film semiconductor 8011 is chosen from single crystal Si andfurther epitaxy of the same species during subsequent deposition 9020forms single crystal regions 9030 seeded by region 8011 and amorphousregions 9025 deposited upon amorphous substrate 8012. The depositedlayers can be chosen to exhibit different conductivity type, such asn-type or p-type. For example, thin film layer 8011 can be deposited asn-type Si and subsequent processing in step 9200 can deposit p-type c-Si9030 and p-type a-Si 9025. The regions can be metallized to formelectrical contacts to the p-type Si region 9030 via contact 9031 andp-type a-Si region 9025 via electrode 9026.

The deposition process used for layers 9025 and 9030 can be viadifferent process, for example, PECVD, CVD and the like, forminghydrogenated amorphous Si (H:a-Si). The hydrogen content can be used asan effective means for passivating junctions between 9025/8011 andsurfaces of 9030. The resulting structure of FIG. 13 comprises a p/ndiode c-Si junction and p-type a-Si/n-type c-Si junction. The band gapenergy variation as a function of direction parallel (x) andperpendicular (y) to the plane of the alternative substrate. The wideband gap a-Si region 9025 forms a structural heterojunction with thec-Si region 8011. The p-type 9030 and n-type 8011 c-Si homojunctionforms a p/n diode.

Operation of structure in FIG. 36 as solar cell energy conversion deviceis achieved by orienting structure such that solar radiation is incidentin a direction substantially from the alternative substrate surface intothe active thin film semiconductor layers. The metallization/electrodescan behave as reflectors enabling multi-pass reflection in thin filmlayers. The a-Si region is responsive to higher energy photons (shorterwavelength ˜600 nm) and the c-Si is responsive to lower energy photons(in the vicinity of the indirect band gap absorption edge>1 eV, i.e.˜1200 nm). The vertical and horizontal diodes formed by the presentinvention constitutes a two junction solar cell with solar cellefficiency exceeding that from single junction c-Si p/n solar cell.

In one embodiment a solar cell device for converting radiation toelectrical energy comprises an active layer for the convertingcomprising at least a large band gap material and a small band gapmaterial and an optically transparent conducting oxide over at least aportion of the surface of the active layer first receiving theradiation.

In some embodiments a device for converting radiation to electricalenergy comprises; active layer for converting incident radiation toelectrical energy comprising a Group IV semiconductor; transparentsubstrate; and transparent barrier layer consisting of one or more arare earth compounds; wherein the barrier layer separates the activelayer and the substrate and substantially prevents unwanted ions fromthe substrate migrating to the active layer wherein the active layercomprises one or more layers of a large band gap material; and one ormore layers of a small band gap material; wherein the large band gapmaterial is chosen from a group consisting of rare-earth oxide(RE_(x)O_(z)), rare-earth germanium oxide (RE_(x)Ge_(y)O_(z)),rare-earth silicon oxide (RE_(x)Si_(y)O_(z)),rare-earth-silicon-oxide-phosphide (RE_(x)Si_(y)O_(z)P_(w)),rare-earth-silicon-oxide-nitride (RE_(x)Si_(y)O_(z)N_(w)),rare-earth-silicon-oxide-nitride-phosphide (RE_(x)Si_(y)O_(z)N_(w)P_(q))wherein X, Z>0 and Y, W, Q are ≧0, such that the band gap is greaterthan about 3 eV and wherein said small band gap material is chosen froma group consisting of rare-earth-silicon (RE_(x)Si_(y)),rare-earth-germanium (RE_(x)Ge_(y)), rare-earth-phosphide (RE_(x)P_(y)),and rare-earth-nitride (RE_(x)N_(y)) and mixtures thereof and wherein X,Y>0 and said small band gap is less than about 3 eV; optionally, theactive layer comprises at least one lateral p-n junction; optionally,the barrier layer consists of one or more rare earth compounds andcharged oxygen vacancies, (O_(y) ^(n)), such that migration of alkalineions across said barrier layer is functionally impeded; optionally, thebarrier layer comprises at least two layers wherein at least one of theat least two layers has a band gap greater than about 3 eV; optionally,the active layer comprises one or more layers of a large band gapmaterial; and one or more layers of a small band gap material; whereinthe large band gap material is chosen from a group consisting ofrare-earth oxide (RE_(x)O_(z)), rare-earth germanium oxide(RE_(x)Ge_(y)O_(z)), rare-earth silicon oxide (RE_(x)Si_(y)O_(z)),rare-earth-silicon-oxide-phosphide (RE_(x)Si_(y)O_(z)P_(w)),rare-earth-silicon-oxide-nitride (RE_(x)Si_(y)O_(z)N_(w)),rare-earth-silicon-oxide-nitride-phosphide (RE_(x)Si_(y)O_(z)N_(w)P_(q))wherein X, Z>0 and Y, W, Q are ≧0, such that the band gap is greaterthan about 3 eV; optionally, the transparent barrier layer consists ofone or more rare earth compounds and at least one charged oxygenvacancy, (O_(y) ^(n); optionally, the small band gap material is chosenfrom a group consisting of rare-earth-silicon (RE_(x)Si_(y)),rare-earth-germanium (RE_(x)Ge_(y)), rare-earth-phosphide (RE_(x)P_(y)),and rare-earth-nitride (RE_(x)N_(y)) and mixtures thereof and wherein X,Y>0 and said small band gap is less than about 3 eV; optionally, thetransparent barrier layer comprises a first and second layer wherein thefirst layer is in contact with the transparent substrate and the secondlayer is in contact with the active layer and wherein at least one ofthe first layer and second layer consists of one or more compoundschosen from a group consisting of calcium oxide (CaO), sodium oxide(Na₂O), potassium oxide (K₂O), aluminum oxide (Al₂O₃), boron oxide(B₂O₃), zirconium oxide (ZrO₂), zircon (ZrSiO₄), lead oxide (PbO),alkaline earth metal oxides (AEOx), phosphate glass, phosphoroussilicate glass, rare-earth sesquioxide (RE₂O₃), rare-earth dioxide(REO₂), rare-earth monoxide (REO), rare-earth nitride (REN), rare-earthoxynitride (REO_(x)N_(y)), rare-earth phosphide (REP), rare-earthoxyphosphide (REO_(x)P_(y)), rare-earth carbide (REC_(y)), rare-earthoxycarbide (REO_(x)C_(y)), aluminum rare-earth oxide(RE_(x)Al_(y)O_(w)), rare-earth aluminosilicate(RE_(x)Al_(y)Si_(z)O_(w)), silicon nitride (SiN_(x)),(Si_(x)Al_(y)N_(z)), N:Al₂O₃, aluminum oxynitride (AlO_(x)N_(y)),aluminum nitride (AlN_(x)), silicon-aluminum-oxynitride(Si_(z)Al_(y)O_(x)N_(y)), silicon-carbon-nitride (Si_(z)C_(x)N_(y)),aluminum-carbon-oxynitride (Al_(z)C_(y)O_(x)N_(y)), silicon, SiO_(x),rare-earth material, germanium and mixtures of silicon-germanium andcombinations and non-stoichiometric combinations thereof; optionally,the transparent barrier layer comprises a first and second layer whereinthe first layer is in contact with the transparent substrate and thesecond layer is in contact with the active layer and wherein the firstlayer consists of one or more a compounds described by[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >O andRE is a rare earth; optionally, the transparent substrate is chosen froma group consisting of sapphire, aluminum oxide (Al₂O₃), diamond (C₄),calcium fluoride (CaF₂), zircon (Zr_(x)Si_(1-x)O₄), zinc oxide (ZnO),aluminum nitride (AlN), glass, sodium-silicate glass(Na₂O)_(x).(SiO₂)_(1-x), alkali-metal oxides (AMO_(x)), alkaline-earthmetal oxides, a ceramic and crystallized bauxite; optionally, thetransparent barrier layer comprises a transparent conducting oxidelayer; optionally, the transparent substrate is flexible.

In some embodiments a device for converting radiation to electricalenergy comprises an active layer for the converting radiation toelectrical energy comprising a first semiconductor layer of firstconductivity type of thickness between about 30 nm and 150 nm; a secondsemiconductor layer of second conductivity type of thickness betweenabout 30 nm and 150 nm; a transparent barrier layer consisting of one ormore a rare earth compounds; and a substrate transparent to a majorityof the radiation for converting, wherein the barrier layer separates theactive layer and the substrate such that migration of deleteriousspecies across the barrier layer is functionally impeded and wherein thefirst and second semiconductor layers comprise one or more layers of alarge band gap material; and one or more layers of a small band gapmaterial; wherein the large band gap material is chosen from a groupconsisting of rare-earth oxide (RE_(x)O_(z)), rare-earth germanium oxide(RE_(x)Ge_(y)O_(z)), rare-earth silicon oxide (RE_(x)Si_(y)O_(z)),rare-earth-silicon-oxide-phosphide (RE_(x)Si_(y)O_(z)P_(w)),rare-earth-silicon-oxide-nitride (RE_(x)Si_(y)O_(z)N_(w)),rare-earth-silicon-oxide-nitride-phosphide (RE_(x)Si_(y)O_(z)N_(w)P_(q))wherein X, Z>0 and Y, W, Q are ≧0, such that the band gap is greaterthan about 3 eV and wherein said small band gap material is chosen froma group consisting of rare-earth-silicon (RE_(x)Si_(y)),rare-earth-germanium (RE_(x)Ge_(y)), rare-earth-phosphide (RE_(x)P_(y)),and rare-earth-nitride (RE_(x)N_(y)) and_mixtures thereof and wherein X,Y>0 and said small band gap is less than about 3 eV; optionally, thesubstrate is chosen from a group consisting of sapphire, aluminum oxide(Al₂O₃), diamond (C₄), calcium fluoride (CaF₂), zircon(Zr_(x)Si_(1-x)O₄), zinc oxide (ZnO), aluminum nitride (AlN), glass,sodium-silicate glass (Na₂O)_(x).(SiO₂)_(1-x), alkali-metal oxides(AMO_(x)), alkaline-earth metal oxides, a ceramic and crystallisedbauxite; optionally, the barrier layer comprises one or more layerswherein at least one of the one or more layers is chosen from a groupconsisting of calcium oxide (CaO), sodium oxide (Na₂O), potassium oxide(K₂O), aluminum oxide (Al₂O₃), boron oxide (B₂O₃), zirconium oxide(ZrO₂), zircon (ZrSiO₄), lead oxide (PbO), alkaline earth metal oxides(AEOx), phosphate glass, phosphorous silicate glass, rare-earthsesquioxide (RE₂O₃), rare-earth dioxide (REO₂), rare-earth monoxide(REO), rare-earth nitride (REN), rare-earth oxynitride (REO_(x)N_(y)),rare-earth phosphide (REP), rare-earth oxyphosphide (REO_(x)P_(y)),rare-earth carbide (REC_(y)), rare-earth oxycarbide (REO_(x)C_(y)),aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)), rare-earthaluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), silicon nitride (SiN_(x)),(Si_(x)Al_(y)N_(z)), N:Al₂O₃, aluminum oxynitride (AlO_(x)N_(y)),aluminum nitride (AlN_(x)), silicon-aluminum-oxynitride(Si_(z)Al_(v)O_(x)N_(y)), silicon-carbon-nitride (Si_(z)C_(x)N_(y)),aluminum-carbon-oxynitride (Al_(z)C_(v)O_(x)N_(y)), silicon, SiO_(x),rare-earth material, germanium and mixtures of silicon-germanium andcombinations and non-stoichiometric combinations thereof; optionally,the active layer comprises a composition chosen from at least one ofsilicon, germanium, and carbon or mixtures thereof.

In some embodiments a device for converting radiation to electricalenergy comprises an active layer for the converting radiation toelectrical energy comprising a first semiconductor layer of firstconductivity type of thickness between about 30 nm and 150 nm; a secondsemiconductor layer of second conductivity type of thickness betweenabout 30 nm and 150 nm; a transparent barrier layer consisting of one ormore rare earth compounds; and a substrate transparent to a majority ofthe radiation for converting, wherein the barrier layer separates theactive layer and the substrate such that migration of deleteriousspecies across the barrier layer is functionally impeded and wherein thefirst and second semiconductor layers comprise one or more layers chosenfrom a group consisting of germanium carbide (GeC_(x)), germaniumnitride (GeN_(x)), tin germanium (SnGe_(x)), tin oxide (SnO_(x)),gallium phosphide (GaP), gallium nitride (GaNx), indium nitride (InNx),aluminium nitride (AlNx), zinc oxide (ZnO_(x)), magnesium oxide(MgO_(x)) and Si_(y)Sn_(y)Ge_(z)C_(w) or combinations andnon-stoichiometric combinations thereof wherein 0<x≦20 and 0<v, y, z≦1and 0≦w≦1; optionally, the first and second semiconductor layerscomprise one or more layers chosen from a group consisting ofZn_(x)Mg_(y)O_(z)N_(w) and non-stoichiometric combinations thereofwherein at least one of x or y is >0 and at least one of z or w is >0;optionally, the first and second semiconductor layers comprise one ormore layers chosen from a group consisting of In_(x)Ga_(y)Al_(z)N_(w)and non-stoichiometric combinations thereof wherein 0<w, y≦1 and 0≦x,z≦1; optionally, the barrier layer comprises at least two layers whereinat least one of the at least two layers has a band gap greater thanabout 3 eV; optionally, the transparent barrier layer comprises a firstand second layer wherein the first layer is in contact with thetransparent substrate and wherein the first layer or second layerconsists of one or more compounds chosen from a group consisting ofcalcium oxide (CaO), sodium oxide (Na₂O), potassium oxide (K₂O),aluminum oxide (Al₂O₃), boron oxide (B₂O₃), zirconium oxide (ZrO₂),zircon (ZrSiO₄), lead oxide (PbO), alkaline earth metal oxides (AEOx),phosphate glass, phosphorous silicate glass, rare-earth sesquioxide(RE₂O₃), rare-earth dioxide (REO₂), rare-earth monoxide (REO),rare-earth nitride (REN), rare-earth oxynitride (REO_(x)N_(y)),rare-earth phosphide (REP), rare-earth oxyphosphide (REO_(x)P_(y)),rare-earth carbide (REC_(y)), rare-earth oxycarbide (REO_(x)C_(y)),aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)), rare-earthaluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), silicon nitride (SiN_(x)),(Si_(x)Al_(y)N_(z)), N:Al₂O₃, aluminum oxynitride (AlO_(x)N_(y)),aluminum nitride (AlN_(x)), silicon-aluminum-oxynitride(Si_(z)AlO_(x)N_(y)), silicon-carbon-nitride (Si_(z)C_(x)N_(y)),aluminum-carbon-oxynitride (Al_(z)C_(v)O_(x)N_(y)), SiO_(x), rare-earthmaterial, mixtures of silicon-germanium and combinations andnon-stoichiometric combinations thereof; optionally, the transparentbarrier layer comprises a first and second layer wherein the first layeris in contact with the transparent substrate and wherein the first layeror second layer consists of one or more compounds chosen from a groupconsisting of[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >0 andRE is a rare earth; optionally, the transparent substrate is chosen froma group consisting of sapphire, aluminum oxide (Al₂O₃), diamond (C₄),calcium fluoride (CaF₂), zircon (Zr_(x)Si_(1-x)O₄), zinc oxide (ZnO),aluminum nitride (AlN), glass, sodium-silicate glass(Na₂O)_(x).(SiO₂)_(1-x), alkali-metal oxides (AMO_(x)), alkaline-earthmetal oxides, a ceramic and crystallized bauxite.

Foregoing described embodiments of the invention are provided asillustrations and descriptions. They are not intended to limit theinvention to precise form described. In particular, it is contemplatedthat functional implementation of invention described herein may beimplemented equivalently. Alternative construction techniques andprocesses are apparent to one knowledgeable with integrated circuit,solar cell, flexible circuit and MEMS technology. Other variations andembodiments are possible in light of above teachings, and it is thusintended that the scope of invention not be limited by this DetailedDescription, but rather by Claims following.

1. A device for converting radiation to electrical energy comprising; anactive layer for the converting radiation to electrical energycomprising a first semiconductor layer of first conductivity type ofthickness between about 30 nm and 150 nm; a second semiconductor layerof second conductivity type of thickness between about 30 nm and 150 nm;a transparent barrier layer consisting of one or more rare earthcompounds; and a substrate transparent to a majority of the radiationfor converting, wherein the barrier layer separates the active layer andthe substrate such that migration of deleterious species across thebarrier layer is functionally impeded and wherein the first and secondsemiconductor layers comprise one or more layers chosen from a groupconsisting of germanium carbide (GeC_(x)), germanium nitride (GeN_(x)),tin germanium (SnGe_(x)), tin oxide (SnO_(x)), gallium phosphide (GaP),gallium nitride (GaNx), indium nitride (InNx), aluminium nitride (AlNx),zinc oxide (ZnO_(x)), magnesium oxide (MgO_(x)) andSi_(v)Sn_(y)Ge_(z)C_(w) or combinations and non-stoichiometriccombinations thereof wherein 0<x≦20 and 0<v, y, z≦1 and 0≦w≦1.
 2. Adevice as in claim 1 wherein the barrier layer comprises at least twolayers wherein at least one of the at least two layers has a band gapgreater than about 3 eV.
 3. A device as in claim 1 wherein thetransparent barrier layer comprises a first and second layer wherein thefirst layer is in contact with the transparent substrate and wherein thefirst layer or second layer consists of one or more compounds chosenfrom a group consisting of calcium oxide (CaO), sodium oxide (Na₂O),potassium oxide (K₂O), aluminum oxide (Al₂O₃), boron oxide (B₂O₃),zirconium oxide (ZrO₂), zircon (ZrSiO₄), lead oxide (PbO), alkalineearth metal oxides (AEOx), phosphate glass, phosphorous silicate glass,rare-earth sesquioxide (RE₂O₃), rare-earth dioxide (REO₂), rare-earthmonoxide (REO), rare-earth nitride (REN), rare-earth oxynitride(REO_(x)N_(y)), rare-earth phosphide (REP), rare-earth oxyphosphide(REO_(x)P_(y)), rare-earth carbide (REC_(y)), rare-earth oxycarbide(REO_(x)C_(y)), aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)),rare-earth aluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), silicon nitride(SiN_(x)), (Si_(x)Al_(y)N_(z)), N:Al₂O₃, aluminum oxynitride(AlO_(x)N_(y)), aluminum nitride (AlN_(x)), silicon-aluminum-oxynitride(Si_(z)Al_(y)O_(x)N_(y)), silicon-carbon-nitride (Si_(z)C_(x)N_(y)),aluminum-carbon-oxynitride (Al_(z)C_(v)O_(x)N_(y)), SiO_(x), rare-earthmaterial, mixtures of silicon-germanium and combinations andnon-stoichiometric combinations thereof.
 4. A device as in claim 1wherein the transparent barrier layer comprises a first and second layerwherein the first layer is in contact with the transparent substrate andwherein the first layer or second layer consists of one or morecompounds chosen from a group consisting of[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >0 andRE is a rare earth.
 5. A device as in claim 1 wherein the transparentsubstrate is chosen from a group consisting of sapphire, aluminum oxide(Al₂O₃), diamond (C₄), calcium fluoride (CaF₂), zircon(Zr_(x)Si_(1-x)O₄), zinc oxide (ZnO), aluminum nitride (AlN), glass,sodium-silicate glass (Na₂O)_(x).(SiO₂)_(1-x), alkali-metal oxides(AMO_(x)), alkaline-earth metal oxides, a ceramic and crystallisedbauxite.
 6. A device for converting radiation to electrical energycomprising; an active layer for the converting radiation to electricalenergy comprising a first semiconductor layer of first conductivity typeof thickness between about 30 nm and 150 nm; a second semiconductorlayer of second conductivity type of thickness between about 30 nm and150 nm; a transparent barrier layer consisting of one or more rare earthcompounds; and a substrate transparent to a majority of the radiationfor converting, wherein the barrier layer separates the active layer andthe substrate such that migration of deleterious species across thebarrier layer is functionally impeded and wherein the first and secondsemiconductor layers comprise one or more layers chosen from a groupconsisting of In_(x)Ga_(y)Al_(z)N_(w) and non-stoichiometriccombinations thereof wherein 0<w, y≦1 and 0≦x, z≦1.
 7. A device as inclaim 6 wherein the barrier layer comprises at least two layers whereinat least one of the at least two layers has a band gap greater thanabout 3 eV.
 8. A device as in claim 6 wherein the transparent barrierlayer comprises a first and second layer wherein the first layer is incontact with the transparent substrate and wherein the first layer orsecond layer consists of one or more compounds chosen from a groupconsisting of calcium oxide (CaO), sodium oxide (Na₂O), potassium oxide(K₂O), aluminum oxide (Al₂O₃), boron oxide (B₂O₃), zirconium oxide(ZrO₂), zircon (ZrSiO₄), lead oxide (PbO), alkaline earth metal oxides(AEOx), phosphate glass, phosphorous silicate glass, rare-earthsesquioxide (RE₂O₃), rare-earth dioxide (REO₂), rare-earth monoxide(REO), rare-earth nitride (REN), rare-earth oxynitride (REO_(x)N_(y)),rare-earth phosphide (REP), rare-earth oxyphosphide (REO_(x)P_(y)),rare-earth carbide (REC_(y)), rare-earth oxycarbide (REO_(x)C_(y)),aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)), rare-earthaluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), silicon nitride (SiN_(x)),(Si_(x)Al_(y)N_(z)), N:Al₂O₃, aluminum oxynitride (AlO_(x)N_(y)),aluminum nitride (AlN_(x)), silicon-aluminum-oxynitride(Si_(z)Al_(y)O_(x)N_(y)), silicon-carbon-nitride (Si_(z)C_(x)N_(y)),aluminum-carbon-oxynitride (Al_(z)C_(v)O_(x)N_(y)), SiO_(x), rare-earthmaterial, mixtures of silicon-germanium and combinations andnon-stoichiometric combinations thereof.
 9. A device as in claim 6wherein the transparent barrier layer comprises a first and second layerwherein the first layer is in contact with the transparent substrate andwherein the first layer or second layer consists of one or morecompounds chosen from a group consisting of[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >0 andRE is a rare earth.
 10. A device as in claim 6 wherein the transparentsubstrate is chosen from a group consisting of sapphire, aluminum oxide(Al₂O₃), diamond (C₄), calcium fluoride (CaF₂), zircon(Zr_(x)Si_(1-x)O₄), zinc oxide (ZnO), aluminum nitride (AlN), glass,sodium-silicate glass (Na₂O)_(x).(SiO₂)_(1-x), alkali-metal oxides(AMO_(x)), alkaline-earth metal oxides, a ceramic and crystallisedbauxite.
 11. A device for converting radiation to electrical energycomprising; an active layer for the converting radiation to electricalenergy comprising a first semiconductor layer of first conductivity typeof thickness between about 30 nm and 150 nm; a second semiconductorlayer of second conductivity type of thickness between about 30 nm and150 nm; a transparent barrier layer consisting of one or more rare earthcompounds; and a substrate transparent to a majority of the radiationfor converting, wherein the barrier layer separates the active layer andthe substrate such that migration of deleterious species across thebarrier layer is functionally impeded and wherein the first and secondsemiconductor layers comprise one or more layers chosen from a groupconsisting of Zn_(x)Mg_(y)O_(z)N_(w) and non-stoichiometric combinationsthereof wherein at least one of x or y is >0 and at least one of z or wis >0.
 12. A device as in claim 11 wherein the barrier layer comprisesat least two layers wherein at least one of the at least two layers hasa band gap greater than about 3 eV.
 13. A device as in claim 11 whereinthe transparent barrier layer comprises a first and second layer whereinthe first layer is in contact with the transparent substrate and whereinthe first layer or second layer consists of one or more compounds chosenfrom a group consisting of calcium oxide (CaO), sodium oxide (Na₂O),potassium oxide (K₂O), aluminum oxide (Al₂O₃), boron oxide (B₂O₃),zirconium oxide (ZrO₂), zircon (ZrSiO₄), lead oxide (PbO), alkalineearth metal oxides (AEOx), phosphate glass, phosphorous silicate glass,rare-earth sesquioxide (RE₂O₃), rare-earth dioxide (REO₂), rare-earthmonoxide (REO), rare-earth nitride (REN), rare-earth oxynitride(REO_(x)N_(y)), rare-earth phosphide (REP), rare-earth oxyphosphide(REO_(x)P_(y)), rare-earth carbide (REC_(y)), rare-earth oxycarbide(REO_(x)C_(y)), aluminum rare-earth oxide (RE_(x)Al_(y)O_(w)),rare-earth aluminosilicate (RE_(x)Al_(y)Si_(z)O_(w)), silicon nitride(SiN_(x)), (Si_(x)Al_(y)N_(z)), N:Al₂O₃, aluminum oxynitride(AlO_(x)N_(y)), aluminum nitride (AlN_(x)), silicon-aluminum-oxynitride(Si_(z)Al_(v)O_(x)N_(y)), silicon-carbon-nitride (Si_(z)C_(x)N_(y)),aluminum-carbon-oxynitride (Al_(z)C_(v)O_(x)N_(y)), SiO_(x), rare-earthmaterial, mixtures of silicon-germanium and combinations andnon-stoichiometric combinations thereof.
 14. A device as in claim 11wherein the transparent barrier layer comprises a first and second layerwherein the first layer is in contact with the transparent substrate andwherein the first layer or second layer consists of one or morecompounds chosen from a group consisting of[RE]_(x)[RE]_(y)[RE]_(z)[C]_(m)[O]_(n)[N]_(p)[P]_(r)[Si]_(s)[Ge]_(t)[Al]_(u)wherein x>0 and at least one of y, z, m, n, p, r, s, t, or u are >0 andRE is a rare earth.
 15. A device as in claim 11 wherein the transparentsubstrate is chosen from a group consisting of sapphire, aluminum oxide(Al₂O₃), diamond (C₄), calcium fluoride (CaF₂), zircon(Zr_(x)Si_(1-x)O₄), zinc oxide (ZnO), aluminum nitride (AlN), glass,sodium-silicate glass (Na₂O)_(x).(SiO₂)_(1-x), alkali-metal oxides(AMO_(x)), alkaline-earth metal oxides, a ceramic and crystallisedbauxite.